diff --git a/app/api/projects/[projectId]/todos/items/[itemId]/route.ts b/app/api/projects/[projectId]/todos/items/[itemId]/route.ts
index 18e31fd..bb9c6a6 100644
--- a/app/api/projects/[projectId]/todos/items/[itemId]/route.ts
+++ b/app/api/projects/[projectId]/todos/items/[itemId]/route.ts
@@ -6,6 +6,23 @@ import { handleApiError, jsonError } from '@/lib/api/handleError';
 
 export const runtime = 'nodejs';
 
+export async function GET(
+  _request: NextRequest,
+  { params }: { params: Promise<{ projectId: string; itemId: string }> }
+) {
+  const user = await getCurrentUser();
+  if (!user) return handleApiError(new UnauthorizedError());
+  const { itemId } = await params;
+  const service = createTodoService();
+  try {
+    const item = service.getItem(user.id, Number(itemId));
+    const attachments = service.getItemAttachments(user.id, Number(itemId));
+    return NextResponse.json({ item, attachments });
+  } catch (error) {
+    return handleApiError(error);
+  }
+}
+
 export async function PATCH(
   request: NextRequest,
   { params }: { params: Promise<{ projectId: string; itemId: string }> }
@@ -35,23 +52,29 @@ export async function PATCH(
       );
       return NextResponse.json({ item });
     }
+    // nullable フィールドは absent(undefined=更新しない) と null(クリア) を区別する
+    const nullableString = (v: unknown): string | null | undefined =>
+      v === undefined ? undefined : v === null ? null : String(v);
+    const nullableNumber = (v: unknown): number | null | undefined =>
+      v === undefined ? undefined : v === null ? null : Number(v);
+
     const item = service.updateItem(user.id, Number(itemId), {
       title: typeof body.title === 'string' ? body.title : undefined,
-      description:
-        typeof body.description === 'string' ? body.description : undefined,
-      assigneeId:
-        body.assigneeId === null || body.assigneeId === undefined
-          ? undefined
-          : Number(body.assigneeId),
+      description: nullableString(body.description),
+      assigneeId: nullableNumber(body.assigneeId),
       priority:
         typeof body.priority === 'string'
           ? (body.priority as 'low' | 'normal' | 'high')
           : undefined,
-      dueDate: typeof body.dueDate === 'string' ? body.dueDate : undefined,
-      milestoneId:
-        body.milestoneId === null || body.milestoneId === undefined
-          ? undefined
-          : Number(body.milestoneId),
+      startDate: nullableString(body.startDate),
+      dueDate: nullableString(body.dueDate),
+      tags: nullableString(body.tags),
+      milestoneId: nullableNumber(body.milestoneId),
+      fileIds: Array.isArray(body.fileIds)
+        ? body.fileIds
+            .map((n) => Number(n))
+            .filter((n) => Number.isFinite(n) && n > 0)
+        : undefined,
     });
     return NextResponse.json({ item });
   } catch (error) {
diff --git a/app/api/projects/[projectId]/todos/items/route.ts b/app/api/projects/[projectId]/todos/items/route.ts
index bc8d040..8149a44 100644
--- a/app/api/projects/[projectId]/todos/items/route.ts
+++ b/app/api/projects/[projectId]/todos/items/route.ts
@@ -38,6 +38,11 @@ export async function POST(
   }
   const service = createTodoService();
   try {
+    const fileIds = Array.isArray(body.fileIds)
+      ? body.fileIds
+          .map((n) => Number(n))
+          .filter((n) => Number.isFinite(n) && n > 0)
+      : [];
     const item = service.createItem(user.id, Number(projectId), {
       title: String(body.title ?? ''),
       columnId: Number(body.columnId ?? 0),
@@ -51,7 +56,11 @@ export async function POST(
         typeof body.priority === 'string'
           ? (body.priority as 'low' | 'normal' | 'high')
           : undefined,
+      startDate:
+        typeof body.startDate === 'string' ? body.startDate : undefined,
       dueDate: typeof body.dueDate === 'string' ? body.dueDate : null,
+      tags: typeof body.tags === 'string' ? body.tags : undefined,
+      fileIds,
     });
     return NextResponse.json({ item }, { status: 201 });
   } catch (error) {
diff --git a/app/projects/[projectId]/todos/page.tsx b/app/projects/[projectId]/todos/page.tsx
index bcb17d6..52f096f 100644
--- a/app/projects/[projectId]/todos/page.tsx
+++ b/app/projects/[projectId]/todos/page.tsx
@@ -31,6 +31,7 @@ export default async function TodosPage({
   const todoService = createTodoService();
   const columns = todoService.getColumns(user.id, project.id);
   const items = todoService.getItems(user.id, project.id);
+  const members = projectService.getMembers(user.id, project.id);
 
   return (
     <div className="min-h-screen bg-gray-50">
@@ -42,6 +43,7 @@ export default async function TodosPage({
           projectId={project.id}
           columns={columns}
           initialItems={items}
+          members={members}
         />
       </main>
     </div>
diff --git a/components/todo/KanbanBoard.tsx b/components/todo/KanbanBoard.tsx
index 546b2f8..e08c36f 100644
--- a/components/todo/KanbanBoard.tsx
+++ b/components/todo/KanbanBoard.tsx
@@ -2,6 +2,8 @@
 
 import { useCallback, useState, type DragEvent } from 'react';
 import type { TodoColumn, TodoItem } from '@/lib/types';
+import type { ProjectMemberWithUser } from '@/repositories/ProjectMemberRepository';
+import { TodoDialog } from '@/components/todo/TodoDialog';
 
 const PRIORITY_COLORS: Record<string, string> = {
   high: 'bg-red-100 text-red-700',
@@ -13,13 +15,16 @@ export function KanbanBoard({
   projectId,
   columns,
   initialItems,
+  members,
 }: {
   projectId: number;
   columns: TodoColumn[];
   initialItems: TodoItem[];
+  members: ProjectMemberWithUser[];
 }) {
   const [items, setItems] = useState<TodoItem[]>(initialItems);
   const [draggingId, setDraggingId] = useState<number | null>(null);
+  const [selectedItem, setSelectedItem] = useState<TodoItem | null>(null);
 
   const reload = useCallback(async () => {
     const res = await fetch(`/api/projects/${projectId}/todos/items`);
@@ -44,7 +49,7 @@ export function KanbanBoard({
       setDraggingId(null);
       return;
     }
-    // 楽観的にローカル更新したあとAPIで移動
+    // 楽観的にローカル更新したあとAPIで移動(失敗時は再取得で巻き戻す)
     setItems((prev) =>
       prev.map((i) => (i.id === itemId ? { ...i, columnId: column.id } : i))
     );
@@ -52,7 +57,9 @@ export function KanbanBoard({
       method: 'PATCH',
       headers: { 'Content-Type': 'application/json' },
       body: JSON.stringify({ columnId: column.id, orderIndex: 0 }),
-    }).then(() => reload());
+    })
+      .catch(() => undefined)
+      .finally(() => reload());
     setDraggingId(null);
   }
 
@@ -91,48 +98,99 @@ export function KanbanBoard({
               {column.name} ({colItems.length})
             </h2>
             <ul className="space-y-2">
-              {colItems.map((item) => (
-                <li
-                  key={item.id}
-                  draggable
-                  onDragStart={(e) => onDragStart(e, item.id)}
-                  className={`cursor-grab rounded border bg-white p-2 shadow-sm ${
-                    draggingId === item.id ? 'opacity-50' : ''
-                  } ${item.completedAt ? 'opacity-60 line-through' : ''}`}
-                  data-testid={`todo-card-${item.id}`}
-                >
-                  <div className="flex items-start justify-between gap-2">
-                    <span className="text-sm">{item.title}</span>
-                    <button
-                      type="button"
-                      onClick={() => toggleComplete(item.id)}
-                      className="text-xs text-blue-600 hover:underline"
-                      data-testid={`todo-complete-${item.id}`}
-                    >
-                      {item.completedAt ? '戻す' : '完了'}
-                    </button>
-                  </div>
-                  <div className="mt-1 flex gap-1">
-                    <span
-                      className={`rounded px-1.5 py-0.5 text-xs ${
-                        PRIORITY_COLORS[item.priority] ?? PRIORITY_COLORS.normal
-                      }`}
-                    >
-                      {item.priority}
-                    </span>
-                    {item.dueDate && (
-                      <span className="text-xs text-gray-500">
-                        期限: {item.dueDate}
+              {colItems.map((item) => {
+                const tags = item.tags
+                  ?.split(',')
+                  .map((t) => t.trim())
+                  .filter(Boolean);
+                const assignee = members.find(
+                  (m) => m.user.id === item.assigneeId
+                );
+                return (
+                  <li
+                    key={item.id}
+                    draggable
+                    onDragStart={(e) => onDragStart(e, item.id)}
+                    onClick={() => setSelectedItem(item)}
+                    className={`cursor-grab rounded border bg-white p-2 shadow-sm ${
+                      draggingId === item.id ? 'opacity-50' : ''
+                    } ${item.completedAt ? 'opacity-60 line-through' : ''}`}
+                    data-testid={`todo-card-${item.id}`}
+                  >
+                    <div className="flex items-start justify-between gap-2">
+                      <span
+                        className="text-sm hover:text-blue-600 hover:underline"
+                        data-testid={`todo-open-${item.id}`}
+                      >
+                        {item.title}
                       </span>
+                      <button
+                        type="button"
+                        onClick={(e) => {
+                          e.stopPropagation();
+                          toggleComplete(item.id);
+                        }}
+                        className="text-xs text-blue-600 hover:underline"
+                        data-testid={`todo-complete-${item.id}`}
+                      >
+                        {item.completedAt ? '戻す' : '完了'}
+                      </button>
+                    </div>
+                    <div className="mt-1 flex flex-wrap items-center gap-1">
+                      <span
+                        className={`rounded px-1.5 py-0.5 text-xs ${
+                          PRIORITY_COLORS[item.priority] ??
+                          PRIORITY_COLORS.normal
+                        }`}
+                      >
+                        {item.priority}
+                      </span>
+                      {item.dueDate && (
+                        <span className="text-xs text-gray-500">
+                          期限: {item.dueDate}
+                        </span>
+                      )}
+                      {item.startDate && (
+                        <span className="text-xs text-gray-400">
+                          開始: {item.startDate}
+                        </span>
+                      )}
+                      {assignee && (
+                        <span className="text-xs text-gray-500">
+                          @{assignee.user.name}
+                        </span>
+                      )}
+                    </div>
+                    {tags && tags.length > 0 && (
+                      <div className="mt-1 flex flex-wrap gap-1">
+                        {tags.map((t) => (
+                          <span
+                            key={t}
+                            className="rounded bg-gray-100 px-1.5 py-0.5 text-[10px] text-gray-600"
+                          >
+                            {t}
+                          </span>
+                        ))}
+                      </div>
                     )}
-                  </div>
-                </li>
-              ))}
+                  </li>
+                );
+              })}
             </ul>
             <NewTaskInput onAdd={(title) => addTask(column.id, title)} />
           </section>
         );
       })}
+
+      {selectedItem && (
+        <TodoDialog
+          projectId={projectId}
+          item={selectedItem}
+          members={members}
+          onClose={() => setSelectedItem(null)}
+          onSaved={reload}
+        />
+      )}
     </div>
   );
 }
diff --git a/components/todo/TodoDialog.tsx b/components/todo/TodoDialog.tsx
new file mode 100644
index 0000000..e4e466c
--- /dev/null
+++ b/components/todo/TodoDialog.tsx
@@ -0,0 +1,311 @@
+'use client';
+
+import { useEffect, useRef, useState } from 'react';
+import type { AttachmentView, TodoItem, TodoPriority } from '@/lib/types';
+import type { ProjectMemberWithUser } from '@/repositories/ProjectMemberRepository';
+import { AttachmentList } from '@/components/files/AttachmentList';
+import {
+  AttachmentPicker,
+  type AttachmentPickerHandle,
+} from '@/components/files/AttachmentPicker';
+
+const PRIORITIES: TodoPriority[] = ['low', 'normal', 'high'];
+
+function parseTags(tags: string | null): string[] {
+  if (!tags) return [];
+  return tags
+    .split(',')
+    .map((t) => t.trim())
+    .filter((t) => t.length > 0);
+}
+
+/**
+ * ToDo編集/詳細ダイアログ。
+ * カードクリックで開き、タイトル/説明/担当/優先度/開始日/期限/タグ/添付を
+ * 編集・閲覧できる。完了日(完了時刻)・作成/更新日時は読み取り専用で表示。
+ */
+export function TodoDialog({
+  projectId,
+  item,
+  members,
+  onClose,
+  onSaved,
+}: {
+  projectId: number;
+  item: TodoItem;
+  members: ProjectMemberWithUser[];
+  onClose: () => void;
+  onSaved: () => void | Promise<void>;
+}) {
+  const [title, setTitle] = useState(item.title);
+  const [description, setDescription] = useState(item.description ?? '');
+  const [assigneeId, setAssigneeId] = useState<string>(
+    item.assigneeId ? String(item.assigneeId) : ''
+  );
+  const [priority, setPriority] = useState<TodoPriority>(item.priority);
+  const [startDate, setStartDate] = useState(item.startDate ?? '');
+  const [dueDate, setDueDate] = useState(item.dueDate ?? '');
+  const [tags, setTags] = useState(item.tags ?? '');
+  const [attachments, setAttachments] = useState<AttachmentView[]>([]);
+  const [current, setCurrent] = useState<TodoItem>(item);
+  const [loading, setLoading] = useState(true);
+  const [saving, setSaving] = useState(false);
+  const [pickerLoading, setPickerLoading] = useState(false);
+  const [error, setError] = useState<string | null>(null);
+  const pickerRef = useRef<AttachmentPickerHandle>(null);
+
+  // 開封時に最新のアイテム+添付を取得
+  useEffect(() => {
+    let alive = true;
+    setLoading(true);
+    fetch(`/api/projects/${projectId}/todos/items/${item.id}`)
+      .then((res) => (res.ok ? res.json() : null))
+      .then((data) => {
+        if (!alive || !data) return;
+        const fetched = data.item as TodoItem;
+        setTitle(fetched.title);
+        setDescription(fetched.description ?? '');
+        setAssigneeId(fetched.assigneeId ? String(fetched.assigneeId) : '');
+        setPriority(fetched.priority);
+        setStartDate(fetched.startDate ?? '');
+        setDueDate(fetched.dueDate ?? '');
+        setTags(fetched.tags ?? '');
+        setAttachments((data.attachments as AttachmentView[]) ?? []);
+        setCurrent(fetched);
+      })
+      .catch(() => undefined)
+      .finally(() => alive && setLoading(false));
+    return () => {
+      alive = false;
+    };
+  }, [projectId, item.id]);
+
+  useEffect(() => {
+    function onKey(e: KeyboardEvent) {
+      if (e.key === 'Escape') onClose();
+    }
+    window.addEventListener('keydown', onKey);
+    return () => window.removeEventListener('keydown', onKey);
+  }, [onClose]);
+
+  async function onSave() {
+    setSaving(true);
+    setError(null);
+    const fileIds = pickerRef.current?.getFileIds() ?? [];
+    const res = await fetch(
+      `/api/projects/${projectId}/todos/items/${item.id}`,
+      {
+        method: 'PATCH',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify({
+          title,
+          description,
+          assigneeId: assigneeId ? Number(assigneeId) : null,
+          priority,
+          startDate: startDate || null,
+          dueDate: dueDate || null,
+          tags: tags || null,
+          fileIds,
+        }),
+      }
+    );
+    setSaving(false);
+    if (res.ok) {
+      pickerRef.current?.clear();
+      await onSaved();
+      onClose();
+    } else {
+      const b = (await res.json().catch(() => null)) as {
+        error?: { message?: string };
+      } | null;
+      setError(b?.error?.message ?? '保存に失敗しました');
+    }
+  }
+
+  const tagList = parseTags(tags);
+
+  return (
+    <div
+      className="fixed inset-0 z-50 flex items-start justify-center bg-black/40 p-4"
+      onClick={onClose}
+      data-testid="todo-dialog-backdrop"
+    >
+      <div
+        className="mt-8 w-full max-w-xl rounded-lg bg-white shadow-xl"
+        onClick={(e) => e.stopPropagation()}
+        role="dialog"
+        aria-modal="true"
+        aria-label={`ToDo ${item.title} の編集`}
+        data-testid="todo-dialog"
+      >
+        <div className="flex items-center justify-between border-b p-4">
+          <h2 className="text-lg font-bold text-gray-800">ToDoの編集</h2>
+          <button
+            type="button"
+            onClick={onClose}
+            className="rounded p-1 text-gray-400 hover:bg-gray-100 hover:text-gray-600"
+            aria-label="閉じる"
+            data-testid="todo-dialog-close"
+          >
+            ×
+          </button>
+        </div>
+
+        {loading ? (
+          <p className="p-6 text-sm text-gray-400">読み込み中...</p>
+        ) : (
+          <div className="max-h-[70vh] space-y-3 overflow-y-auto p-4">
+            <div>
+              <label className="block text-sm font-medium">タイトル</label>
+              <input
+                type="text"
+                value={title}
+                onChange={(e) => setTitle(e.target.value)}
+                className="mt-1 w-full rounded border px-3 py-2"
+                data-testid="todo-title"
+              />
+            </div>
+            <div>
+              <label className="block text-sm font-medium">説明</label>
+              <textarea
+                value={description}
+                onChange={(e) => setDescription(e.target.value)}
+                className="mt-1 min-h-[80px] w-full rounded border px-3 py-2"
+                data-testid="todo-description"
+              />
+            </div>
+            <div className="grid grid-cols-2 gap-3">
+              <div>
+                <label className="block text-sm font-medium">担当者</label>
+                <select
+                  value={assigneeId}
+                  onChange={(e) => setAssigneeId(e.target.value)}
+                  className="mt-1 w-full rounded border px-3 py-2"
+                  data-testid="todo-assignee"
+                >
+                  <option value="">未割当</option>
+                  {members.map((m) => (
+                    <option key={m.user.id} value={String(m.user.id)}>
+                      {m.user.name}
+                    </option>
+                  ))}
+                </select>
+              </div>
+              <div>
+                <label className="block text-sm font-medium">優先度</label>
+                <select
+                  value={priority}
+                  onChange={(e) => setPriority(e.target.value as TodoPriority)}
+                  className="mt-1 w-full rounded border px-3 py-2"
+                  data-testid="todo-priority"
+                >
+                  {PRIORITIES.map((p) => (
+                    <option key={p} value={p}>
+                      {p}
+                    </option>
+                  ))}
+                </select>
+              </div>
+            </div>
+            <div className="grid grid-cols-2 gap-3">
+              <div>
+                <label className="block text-sm font-medium">開始日</label>
+                <input
+                  type="date"
+                  value={startDate}
+                  onChange={(e) => setStartDate(e.target.value)}
+                  className="mt-1 w-full rounded border px-3 py-2"
+                  data-testid="todo-start-date"
+                />
+              </div>
+              <div>
+                <label className="block text-sm font-medium">
+                  期限 (deadline)
+                </label>
+                <input
+                  type="date"
+                  value={dueDate}
+                  onChange={(e) => setDueDate(e.target.value)}
+                  className="mt-1 w-full rounded border px-3 py-2"
+                  data-testid="todo-due-date"
+                />
+              </div>
+            </div>
+            <div>
+              <label className="block text-sm font-medium">
+                タグ (カンマ区切り)
+              </label>
+              <input
+                type="text"
+                value={tags}
+                onChange={(e) => setTags(e.target.value)}
+                placeholder="frontend, urgent"
+                className="mt-1 w-full rounded border px-3 py-2"
+                data-testid="todo-tags"
+              />
+              {tagList.length > 0 && (
+                <div className="mt-1 flex flex-wrap gap-1">
+                  {tagList.map((t) => (
+                    <span
+                      key={t}
+                      className="rounded bg-gray-100 px-2 py-0.5 text-xs text-gray-600"
+                    >
+                      {t}
+                    </span>
+                  ))}
+                </div>
+              )}
+            </div>
+
+            <div>
+              <p className="mb-1 text-sm font-medium">添付ファイル</p>
+              {attachments.length > 0 ? (
+                <AttachmentList attachments={attachments} />
+              ) : (
+                <p className="text-xs text-gray-400">添付なし</p>
+              )}
+              <div className="mt-2">
+                <AttachmentPicker
+                  ref={pickerRef}
+                  projectId={projectId}
+                  onLoadingChange={setPickerLoading}
+                />
+              </div>
+            </div>
+
+            <div className="space-y-1 border-t pt-3 text-xs text-gray-500">
+              <p>完了日時: {current.completedAt ?? '未完了'}</p>
+              <p>作成: {current.createdAt}</p>
+              <p>更新: {current.updatedAt}</p>
+            </div>
+
+            {error && (
+              <p className="text-sm text-red-600" role="alert">
+                {error}
+              </p>
+            )}
+          </div>
+        )}
+
+        <div className="flex justify-end gap-2 border-t p-4">
+          <button
+            type="button"
+            onClick={onClose}
+            className="rounded border px-4 py-2 text-sm text-gray-600 hover:bg-gray-100"
+          >
+            キャンセル
+          </button>
+          <button
+            type="button"
+            onClick={onSave}
+            disabled={saving || pickerLoading || loading}
+            className="rounded bg-blue-600 px-4 py-2 text-sm font-medium text-white hover:bg-blue-700 disabled:opacity-50"
+            data-testid="todo-save"
+          >
+            {saving ? '保存中...' : '保存'}
+          </button>
+        </div>
+      </div>
+    </div>
+  );
+}
diff --git a/docs/functional-design.md b/docs/functional-design.md
index 2c5a4c7..df434ee 100644
--- a/docs/functional-design.md
+++ b/docs/functional-design.md
@@ -200,6 +200,7 @@ interface TodoItem {
   completedAt: string | null;
   orderIndex: number;
   milestoneId: number | null;   // FK milestones.id
+  tags: string | null;          // カンマ区切りのタグ(project_notes.tags と同じ方式)
   createdAt: string;
   updatedAt: string;
   deletedAt: string | null;
@@ -219,9 +220,31 @@ interface FileAsset {
   mimeType: string;             // MIMEタイプ（アップロード時チェック）
   size: number;                 // バイト数
   path: string;                 // ローカルパス（uploads/...）
+  source: FileAssetSource;      // 'library'(Files一覧公開) | 'attachment'(添付専用)
   createdAt: string;
   deletedAt: string | null;
 }
+type FileAssetSource = 'library' | 'attachment';
+```
+
+### attachments
+
+```typescript
+// file_assets とチャット/掲示板/ToDo を多対多で紐付ける
+interface Attachment {
+  id: number;
+  projectId: number;            // FK projects.id ON DELETE CASCADE
+  fileId: number;               // FK file_assets.id
+  targetType: AttachmentTargetType;
+  targetId: number;             // targetType に応じた chat_message/board_thread/board_comment/todo_item の id
+  createdAt: string;
+  deletedAt: string | null;
+}
+type AttachmentTargetType =
+  | 'chat_message'
+  | 'board_thread'
+  | 'board_comment'
+  | 'todo_item';
 ```
 
 ### project_notes
@@ -410,6 +433,7 @@ erDiagram
         integer assignee_id FK
         integer milestone_id FK
         text due_date
+        text tags
     }
     meetings {
         integer id PK
diff --git a/docs/repository-structure.md b/docs/repository-structure.md
index 1c431a9..efaa033 100644
--- a/docs/repository-structure.md
+++ b/docs/repository-structure.md
@@ -235,7 +235,7 @@ components/
 ├── project/             # ProjectCard, DashboardWidget
 ├── board/               # ThreadList, ThreadForm, CommentList
 ├── chat/                # ChatWindow, MessageInput, MessageList
-├── todo/                # KanbanBoard, KanbanColumn, TodoCard
+├── todo/                # KanbanBoard, TodoDialog
 ├── files/               # FileList, Uploader, Lightbox, AttachmentList, AttachmentPicker
 ├── calendar/            # CalendarView, MonthView, WeekView, DayView, EventDetailDialog, CalendarEventForm
 ├── meetings/            # MeetingForm, ConflictWarning
diff --git a/lib/api/services.ts b/lib/api/services.ts
index 6c38e70..cc3fcb9 100644
--- a/lib/api/services.ts
+++ b/lib/api/services.ts
@@ -98,12 +98,19 @@ export function createChatService(): ChatService {
 
 export function createTodoService(): TodoService {
   const db = getDb();
+  const memberRepo = new ProjectMemberRepository(db);
   return new TodoService(
     new TodoRepository(db),
-    new ProjectMemberRepository(db),
+    memberRepo,
     new NotificationService(new NotificationRepository(db)),
     new ActivityLogService(new ActivityLogRepository(db)),
-    getSseHub()
+    getSseHub(),
+    new AttachmentService(
+      new AttachmentRepository(db),
+      new FileRepository(db),
+      memberRepo
+    ),
+    db
   );
 }
 
diff --git a/lib/db/migrations/003_todo_tags.sql b/lib/db/migrations/003_todo_tags.sql
new file mode 100644
index 0000000..c53af38
--- /dev/null
+++ b/lib/db/migrations/003_todo_tags.sql
@@ -0,0 +1,4 @@
+-- 003_todo_tags.sql
+-- ToDoアイテムにタグ列を追加(カンマ区切り、project_notes.tags と同じ方式)。
+
+ALTER TABLE todo_items ADD COLUMN tags TEXT;
diff --git a/lib/types/index.ts b/lib/types/index.ts
index 1f8ae70..cd07525 100644
--- a/lib/types/index.ts
+++ b/lib/types/index.ts
@@ -127,6 +127,7 @@ export interface TodoItem {
   completedAt: string | null;
   orderIndex: number;
   milestoneId: number | null;
+  tags: string | null;
   createdAt: string;
   updatedAt: string;
   deletedAt: string | null;
@@ -153,7 +154,8 @@ export type FileAssetSource = 'library' | 'attachment';
 export type AttachmentTargetType =
   | 'chat_message'
   | 'board_thread'
-  | 'board_comment';
+  | 'board_comment'
+  | 'todo_item';
 
 /** attachments エンティティ。 */
 export interface Attachment {
diff --git a/repositories/MilestoneRepository.ts b/repositories/MilestoneRepository.ts
index c0e7108..39ce1cc 100644
--- a/repositories/MilestoneRepository.ts
+++ b/repositories/MilestoneRepository.ts
@@ -1,5 +1,10 @@
 import type { SqliteDatabase } from '@/lib/db/sqlite';
-import type { Milestone, MilestoneStatus, TodoItem } from '@/lib/types';
+import type {
+  Milestone,
+  MilestoneStatus,
+  TodoItem,
+  TodoPriority,
+} from '@/lib/types';
 
 interface MilestoneRow {
   id: number;
@@ -27,6 +32,7 @@ interface TodoItemRow {
   completed_at: string | null;
   order_index: number;
   milestone_id: number | null;
+  tags: string | null;
   created_at: string;
   updated_at: string;
   deleted_at: string | null;
@@ -55,12 +61,13 @@ function mapTodo(row: TodoItemRow): TodoItem {
     description: row.description,
     assigneeId: row.assignee_id,
     creatorId: row.creator_id,
-    priority: row.priority as never,
+    priority: row.priority as TodoPriority,
     startDate: row.start_date,
     dueDate: row.due_date,
     completedAt: row.completed_at,
     orderIndex: row.order_index,
     milestoneId: row.milestone_id,
+    tags: row.tags,
     createdAt: row.created_at,
     updatedAt: row.updated_at,
     deletedAt: row.deleted_at,
diff --git a/repositories/TodoRepository.ts b/repositories/TodoRepository.ts
index bc5a6bf..a900bac 100644
--- a/repositories/TodoRepository.ts
+++ b/repositories/TodoRepository.ts
@@ -24,6 +24,7 @@ interface TodoItemRow {
   completed_at: string | null;
   order_index: number;
   milestone_id: number | null;
+  tags: string | null;
   created_at: string;
   updated_at: string;
   deleted_at: string | null;
@@ -55,6 +56,7 @@ function mapItem(row: TodoItemRow): TodoItem {
     completedAt: row.completed_at,
     orderIndex: row.order_index,
     milestoneId: row.milestone_id,
+    tags: row.tags,
     createdAt: row.created_at,
     updatedAt: row.updated_at,
     deletedAt: row.deleted_at,
@@ -75,7 +77,9 @@ export interface CreateItemInput {
   description?: string | null;
   assigneeId?: number | null;
   priority?: TodoPriority;
+  startDate?: string | null;
   dueDate?: string | null;
+  tags?: string | null;
   orderIndex: number;
 }
 
@@ -84,7 +88,9 @@ export interface UpdateItemInput {
   description?: string | null;
   assigneeId?: number | null;
   priority?: TodoPriority;
+  startDate?: string | null;
   dueDate?: string | null;
+  tags?: string | null;
   completedAt?: string | null;
   columnId?: number;
   orderIndex?: number;
@@ -193,8 +199,8 @@ export class TodoRepository {
   createItem(input: CreateItemInput): TodoItem {
     const now = new Date().toISOString();
     const result = this.db.execute(
-      `INSERT INTO todo_items (project_id, column_id, title, description, assignee_id, creator_id, priority, start_date, due_date, completed_at, order_index, milestone_id, created_at, updated_at, deleted_at)
-       VALUES (@projectId, @columnId, @title, @description, @assigneeId, @creatorId, @priority, NULL, @dueDate, NULL, @orderIndex, @milestoneId, @createdAt, @updatedAt, NULL)`,
+      `INSERT INTO todo_items (project_id, column_id, title, description, assignee_id, creator_id, priority, start_date, due_date, completed_at, order_index, milestone_id, tags, created_at, updated_at, deleted_at)
+       VALUES (@projectId, @columnId, @title, @description, @assigneeId, @creatorId, @priority, @startDate, @dueDate, NULL, @orderIndex, @milestoneId, @tags, @createdAt, @updatedAt, NULL)`,
       {
         projectId: input.projectId,
         columnId: input.columnId,
@@ -203,9 +209,11 @@ export class TodoRepository {
         assigneeId: input.assigneeId ?? null,
         creatorId: input.creatorId,
         priority: input.priority ?? 'normal',
+        startDate: input.startDate ?? null,
         dueDate: input.dueDate ?? null,
         orderIndex: input.orderIndex,
         milestoneId: null,
+        tags: input.tags ?? null,
         createdAt: now,
         updatedAt: now,
       }
@@ -237,10 +245,18 @@ export class TodoRepository {
       fields.push('priority = @priority');
       params.priority = input.priority;
     }
+    if (input.startDate !== undefined) {
+      fields.push('start_date = @startDate');
+      params.startDate = input.startDate;
+    }
     if (input.dueDate !== undefined) {
       fields.push('due_date = @dueDate');
       params.dueDate = input.dueDate;
     }
+    if (input.tags !== undefined) {
+      fields.push('tags = @tags');
+      params.tags = input.tags;
+    }
     if (input.completedAt !== undefined) {
       fields.push('completed_at = @completedAt');
       params.completedAt = input.completedAt;
diff --git a/services/TodoService.ts b/services/TodoService.ts
index b9d88ac..4c15cbb 100644
--- a/services/TodoService.ts
+++ b/services/TodoService.ts
@@ -2,9 +2,16 @@ import { TodoRepository } from '@/repositories/TodoRepository';
 import { ProjectMemberRepository } from '@/repositories/ProjectMemberRepository';
 import { NotificationService } from '@/services/NotificationService';
 import { ActivityLogService } from '@/services/ActivityLogService';
+import { AttachmentService } from '@/services/AttachmentService';
 import { SseHub } from '@/lib/sse/hub';
+import type { SqliteDatabase } from '@/lib/db/sqlite';
 import { ForbiddenError, NotFoundError, ValidationError } from '@/lib/errors';
-import type { TodoColumn, TodoItem, TodoPriority } from '@/lib/types';
+import type {
+  AttachmentView,
+  TodoColumn,
+  TodoItem,
+  TodoPriority,
+} from '@/lib/types';
 
 const STANDARD_COLUMNS = ['Backlog', 'To Do', 'In Progress', 'Review', 'Done'];
 const VALID_PRIORITIES: TodoPriority[] = ['low', 'normal', 'high'];
@@ -15,7 +22,10 @@ export interface CreateItemInput {
   description?: string;
   assigneeId?: number | null;
   priority?: TodoPriority;
+  startDate?: string | null;
   dueDate?: string | null;
+  tags?: string | null;
+  fileIds?: number[];
 }
 
 export interface UpdateItemRequest {
@@ -23,16 +33,20 @@ export interface UpdateItemRequest {
   description?: string | null;
   assigneeId?: number | null;
   priority?: TodoPriority;
+  startDate?: string | null;
   dueDate?: string | null;
+  tags?: string | null;
   columnId?: number;
   orderIndex?: number;
   milestoneId?: number | null;
+  fileIds?: number[];
 }
 
 /**
  * ToDo/Kanbanの業務ロジックを担うService。
  * 標準カラム初期生成、権限チェック、タスクCRUD/移動/完了、
- * 担当者割当時の通知(todo_assigned)とアクティビティログ(todo_*)、SSE配信を行う。
+ * 担当者割当時の通知(todo_assigned)とアクティビティログ(todo_*)、
+ * 添付ファイル紐付け、SSE配信を行う。
  */
 export class TodoService {
   constructor(
@@ -40,7 +54,9 @@ export class TodoService {
     private readonly projectMemberRepository: ProjectMemberRepository,
     private readonly notificationService: NotificationService,
     private readonly activityLogService: ActivityLogService,
-    private readonly sseHub: SseHub
+    private readonly sseHub: SseHub,
+    private readonly attachmentService: AttachmentService,
+    private readonly db: SqliteDatabase
   ) {}
 
   getColumns(actorId: number, projectId: number): TodoColumn[] {
@@ -119,20 +135,33 @@ export class TodoService {
     if (input.priority && !VALID_PRIORITIES.includes(input.priority)) {
       throw new ValidationError('無効な優先度です', 'priority');
     }
-    const orderIndex =
-      input.columnId !== undefined
-        ? this.todoRepository.maxItemOrderIndex(input.columnId) + 1
-        : 0;
-    const item = this.todoRepository.createItem({
-      projectId,
-      columnId: input.columnId,
-      title: input.title,
-      creatorId: actorId,
-      description: input.description ?? null,
-      assigneeId: input.assigneeId ?? null,
-      priority: input.priority,
-      dueDate: input.dueDate ?? null,
-      orderIndex,
+    // タスク本体と添付紐付けはトランザクション内で一貫保存する
+    const item = this.db.transaction(() => {
+      const orderIndex =
+        this.todoRepository.maxItemOrderIndex(input.columnId) + 1;
+      const created = this.todoRepository.createItem({
+        projectId,
+        columnId: input.columnId,
+        title: input.title,
+        creatorId: actorId,
+        description: input.description ?? null,
+        assigneeId: input.assigneeId ?? null,
+        priority: input.priority,
+        startDate: input.startDate ?? null,
+        dueDate: input.dueDate ?? null,
+        tags: input.tags ?? null,
+        orderIndex,
+      });
+      if (input.fileIds && input.fileIds.length > 0) {
+        this.attachmentService.attach(
+          actorId,
+          projectId,
+          'todo_item',
+          created.id,
+          input.fileIds
+        );
+      }
+      return created;
     });
 
     if (input.assigneeId && input.assigneeId !== actorId) {
@@ -155,7 +184,19 @@ export class TodoService {
       throw new ValidationError('無効な優先度です', 'priority');
     }
     const previousAssignee = item.assigneeId;
-    const updated = this.todoRepository.updateItem(itemId, input);
+    const updated = this.db.transaction(() => {
+      const u = this.todoRepository.updateItem(itemId, input);
+      if (u && input.fileIds && input.fileIds.length > 0) {
+        this.attachmentService.attach(
+          actorId,
+          item.projectId,
+          'todo_item',
+          itemId,
+          input.fileIds
+        );
+      }
+      return u;
+    });
     if (!updated) throw new NotFoundError('TodoItem', itemId);
 
     if (
@@ -220,10 +261,29 @@ export class TodoService {
     if (item.creatorId !== actorId && role !== 'admin') {
       throw new ForbiddenError('作成者または管理者のみ削除できます');
     }
-    this.todoRepository.deleteItem(itemId);
+    this.db.transaction(() => {
+      this.attachmentService.detach('todo_item', itemId);
+      this.todoRepository.deleteItem(itemId);
+    });
     this.broadcastTodo(item.projectId);
   }
 
+  /** 単一のToDoアイテムを取得(メンバーシップチェック付き)。 */
+  getItem(actorId: number, itemId: number): TodoItem {
+    const item = this.todoRepository.findItemById(itemId);
+    if (!item) throw new NotFoundError('TodoItem', itemId);
+    this.requireMember(item.projectId, actorId);
+    return item;
+  }
+
+  /** ToDoに紐付く添付ファイル一覧を取得(メンバーシップチェック付き)。 */
+  getItemAttachments(actorId: number, itemId: number): AttachmentView[] {
+    const item = this.todoRepository.findItemById(itemId);
+    if (!item) throw new NotFoundError('TodoItem', itemId);
+    this.requireMember(item.projectId, actorId);
+    return this.attachmentService.listViews('todo_item', itemId);
+  }
+
   private requireMember(projectId: number, actorId: number): void {
     if (!this.projectMemberRepository.isMember(projectId, actorId)) {
       throw new ForbiddenError('プロジェクトに参加していません');
diff --git a/tests/e2e/todo-kanban.spec.ts b/tests/e2e/todo-kanban.spec.ts
index 8309566..7eef379 100644
--- a/tests/e2e/todo-kanban.spec.ts
+++ b/tests/e2e/todo-kanban.spec.ts
@@ -76,4 +76,99 @@ test.describe('todo / kanban', () => {
       page.getByTestId(`kanban-column-${done.id}`).getByText(title)
     ).toBeVisible();
   });
+
+  test('edit dialog shows and persists metadata + file attachments', async ({
+    page,
+  }) => {
+    const projectId = await setupOwner(page);
+
+    const colsRes = await page.request.get(
+      `/api/projects/${projectId}/todos/columns`
+    );
+    const cols = (
+      (await colsRes.json()) as { columns: { id: number; name: string }[] }
+    ).columns;
+    const backlog = cols.find((c) => c.name === 'Backlog')!;
+
+    // オーナー(担当者候補)のuser idを取得
+    const members = (
+      (await (
+        await page.request.get(`/api/projects/${projectId}/members`)
+      ).json()) as { members: { user: { id: number; name: string } }[] }
+    ).members;
+    const ownerId = members[0].user.id;
+
+    // タスク作成(API)
+    const title = unique('Task');
+    const createRes = await page.request.post(
+      `/api/projects/${projectId}/todos/items`,
+      { data: { title, columnId: backlog.id } }
+    );
+    const { item } = (await createRes.json()) as { item: { id: number } };
+
+    // 添付ファイル(1x1 PNG)をアップロード
+    const png = Buffer.from(
+      'iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNkYAAAAAYAAjCB0C8AAAAASUVORK5CYII=',
+      'base64'
+    );
+    const upRes = await page.request.post(
+      `/api/projects/${projectId}/attachments`,
+      {
+        multipart: {
+          file: { name: 'pic.png', mimeType: 'image/png', buffer: png },
+        },
+      }
+    );
+    expect(upRes.ok()).toBeTruthy();
+    const { file } = (await upRes.json()) as { file: { id: number } };
+
+    // ダイアログを開いてメタデータを編集
+    await page.goto(`/projects/${projectId}/todos`);
+    await page.getByTestId(`todo-card-${item.id}`).click();
+    await expect(page.getByTestId('todo-dialog')).toBeVisible();
+    await page.getByTestId('todo-description').fill('detailed desc');
+    await page.getByTestId('todo-tags').fill('frontend, urgent');
+    await page.getByTestId('todo-start-date').fill('2026-07-01');
+    await page.getByTestId('todo-due-date').fill('2026-07-31');
+    await page.getByTestId('todo-assignee').selectOption(String(ownerId));
+    await page.getByTestId('todo-save').click();
+    await expect(page.getByTestId('todo-dialog')).toBeHidden();
+
+    // カードにタグが表示される
+    await expect(page.getByText('frontend')).toBeVisible();
+
+    // APIでファイルを添付付け
+    const attachRes = await page.request.patch(
+      `/api/projects/${projectId}/todos/items/${item.id}`,
+      { data: { fileIds: [file.id] } }
+    );
+    expect(attachRes.ok()).toBeTruthy();
+
+    // GET でアイテム+添付が取得できる
+    const getRes = await page.request.get(
+      `/api/projects/${projectId}/todos/items/${item.id}`
+    );
+    const body = (await getRes.json()) as {
+      item: {
+        description: string;
+        tags: string;
+        startDate: string;
+        dueDate: string;
+        assigneeId: number;
+      };
+      attachments: { fileId: number }[];
+    };
+    expect(body.item.description).toBe('detailed desc');
+    expect(body.item.tags).toBe('frontend, urgent');
+    expect(body.item.startDate).toBe('2026-07-01');
+    expect(body.item.dueDate).toBe('2026-07-31');
+    expect(body.item.assigneeId).toBe(ownerId);
+    expect(body.attachments).toHaveLength(1);
+
+    // ダイアログ再オープンで添付画像が表示される
+    await page.reload();
+    await page.getByTestId(`todo-card-${item.id}`).click();
+    await expect(page.getByTestId('todo-dialog')).toBeVisible();
+    await expect(page.getByTestId('attachment-list')).toBeVisible();
+  });
 });
diff --git a/tests/unit/lib/db/migrator.test.ts b/tests/unit/lib/db/migrator.test.ts
index 36c1298..c7e30f1 100644
--- a/tests/unit/lib/db/migrator.test.ts
+++ b/tests/unit/lib/db/migrator.test.ts
@@ -182,6 +182,7 @@ describe('Migrator', () => {
     expect(migrator.getAppliedMigrations().map((m) => m.filename)).toEqual([
       '001_initial.sql',
       '002_attachments.sql',
+      '003_todo_tags.sql',
     ]);
   });
 });
diff --git a/tests/unit/repositories/TodoRepository.test.ts b/tests/unit/repositories/TodoRepository.test.ts
index 545643e..0699d05 100644
--- a/tests/unit/repositories/TodoRepository.test.ts
+++ b/tests/unit/repositories/TodoRepository.test.ts
@@ -114,6 +114,49 @@ describe('TodoRepository', () => {
     expect(updated?.completedAt).toBeTruthy();
   });
 
+  it('persists startDate and tags on create', () => {
+    const item = repo.createItem({
+      projectId,
+      columnId,
+      title: 't',
+      creatorId: userId,
+      orderIndex: 0,
+      startDate: '2026-07-01',
+      tags: 'frontend,urgent',
+    });
+    const found = repo.findItemById(item.id);
+    expect(found?.startDate).toBe('2026-07-01');
+    expect(found?.tags).toBe('frontend,urgent');
+  });
+
+  it('updates startDate and tags', () => {
+    const item = repo.createItem({
+      projectId,
+      columnId,
+      title: 't',
+      creatorId: userId,
+      orderIndex: 0,
+    });
+    const updated = repo.updateItem(item.id, {
+      startDate: '2026-08-01',
+      tags: 'backend',
+    });
+    expect(updated?.startDate).toBe('2026-08-01');
+    expect(updated?.tags).toBe('backend');
+  });
+
+  it('defaults startDate and tags to null when omitted', () => {
+    const item = repo.createItem({
+      projectId,
+      columnId,
+      title: 't',
+      creatorId: userId,
+      orderIndex: 0,
+    });
+    expect(item.startDate).toBeNull();
+    expect(item.tags).toBeNull();
+  });
+
   it('isolates items by project', () => {
     const p2 = new ProjectRepository(db).create({
       name: 'P2',
diff --git a/tests/unit/services/TodoService.test.ts b/tests/unit/services/TodoService.test.ts
index b0773af..627e705 100644
--- a/tests/unit/services/TodoService.test.ts
+++ b/tests/unit/services/TodoService.test.ts
@@ -5,10 +5,13 @@ import { UserRepository } from '@/repositories/UserRepository';
 import { ProjectRepository } from '@/repositories/ProjectRepository';
 import { ProjectMemberRepository } from '@/repositories/ProjectMemberRepository';
 import { TodoRepository } from '@/repositories/TodoRepository';
+import { FileRepository } from '@/repositories/FileRepository';
+import { AttachmentRepository } from '@/repositories/AttachmentRepository';
 import { NotificationRepository } from '@/repositories/NotificationRepository';
 import { ActivityLogRepository } from '@/repositories/ActivityLogRepository';
 import { NotificationService } from '@/services/NotificationService';
 import { ActivityLogService } from '@/services/ActivityLogService';
+import { AttachmentService } from '@/services/AttachmentService';
 import { TodoService } from '@/services/TodoService';
 import { SseHub } from '@/lib/sse/hub';
 import { ForbiddenError, NotFoundError } from '@/lib/errors';
@@ -24,7 +27,13 @@ function makeService(db: SqliteDatabase) {
       members,
       new NotificationService(new NotificationRepository(db)),
       new ActivityLogService(new ActivityLogRepository(db)),
-      hub
+      hub,
+      new AttachmentService(
+        new AttachmentRepository(db),
+        new FileRepository(db),
+        members
+      ),
+      db
     ),
     members,
     users,
@@ -161,4 +170,142 @@ describe('TodoService', () => {
       NotFoundError
     );
   });
+
+  it('createItem persists startDate/tags and attaches files', () => {
+    const col = service.getColumns(authorId, projectId)[0];
+    const fileRepo = new FileRepository(db);
+    const f1 = fileRepo.create({
+      projectId,
+      uploaderId: authorId,
+      filename: 'a.png',
+      originalName: 'a.png',
+      mimeType: 'image/png',
+      size: 1,
+      path: '/tmp/a.png',
+      source: 'attachment',
+    });
+    const item = service.createItem(authorId, projectId, {
+      title: 'rich',
+      columnId: col.id,
+      startDate: '2026-07-01',
+      dueDate: '2026-07-31',
+      tags: 'frontend,urgent',
+      fileIds: [f1.id],
+    });
+    expect(item.startDate).toBe('2026-07-01');
+    expect(item.tags).toBe('frontend,urgent');
+    expect(service.getItemAttachments(authorId, item.id)).toHaveLength(1);
+  });
+
+  it('updateItem updates startDate/tags and attaches new files', () => {
+    const col = service.getColumns(authorId, projectId)[0];
+    const item = service.createItem(authorId, projectId, {
+      title: 't',
+      columnId: col.id,
+    });
+    const fileRepo = new FileRepository(db);
+    const f1 = fileRepo.create({
+      projectId,
+      uploaderId: authorId,
+      filename: 'b.png',
+      originalName: 'b.png',
+      mimeType: 'image/png',
+      size: 1,
+      path: '/tmp/b.png',
+      source: 'attachment',
+    });
+    const updated = service.updateItem(authorId, item.id, {
+      description: 'desc',
+      startDate: '2026-08-01',
+      tags: 'backend',
+      fileIds: [f1.id],
+    });
+    expect(updated.description).toBe('desc');
+    expect(updated.startDate).toBe('2026-08-01');
+    expect(updated.tags).toBe('backend');
+    expect(service.getItemAttachments(authorId, item.id)).toHaveLength(1);
+  });
+
+  it('deleteItem detaches its attachments', () => {
+    const col = service.getColumns(authorId, projectId)[0];
+    const fileRepo = new FileRepository(db);
+    const f1 = fileRepo.create({
+      projectId,
+      uploaderId: authorId,
+      filename: 'a.png',
+      originalName: 'a.png',
+      mimeType: 'image/png',
+      size: 1,
+      path: '/tmp/a.png',
+      source: 'attachment',
+    });
+    const item = service.createItem(authorId, projectId, {
+      title: 't',
+      columnId: col.id,
+      fileIds: [f1.id],
+    });
+    expect(service.getItemAttachments(authorId, item.id)).toHaveLength(1);
+    service.deleteItem(authorId, item.id);
+    expect(
+      new AttachmentRepository(db).findByTarget('todo_item', item.id)
+    ).toHaveLength(0);
+  });
+
+  it('getItem and getItemAttachments enforce membership', () => {
+    const col = service.getColumns(authorId, projectId)[0];
+    const item = service.createItem(authorId, projectId, {
+      title: 't',
+      columnId: col.id,
+    });
+    expect(service.getItem(authorId, item.id).id).toBe(item.id);
+    expect(() => service.getItem(outsiderId, item.id)).toThrow(ForbiddenError);
+    expect(() => service.getItemAttachments(outsiderId, item.id)).toThrow(
+      ForbiddenError
+    );
+  });
+
+  it('only the creator or an admin can delete an item (member-but-not-creator cannot)', () => {
+    const col = service.getColumns(authorId, projectId)[0];
+    // authorId(admin)が作成したアイテムを memberId(非管理者・非作成者)は削除できない
+    const item = service.createItem(authorId, projectId, {
+      title: 't',
+      columnId: col.id,
+    });
+    expect(() => service.deleteItem(memberId, item.id)).toThrow(ForbiddenError);
+    // admin(作成者)は削除可
+    service.deleteItem(authorId, item.id);
+    expect(() => service.getItem(authorId, item.id)).toThrow(NotFoundError);
+  });
+
+  it('deleteColumn: admin can delete, non-admin member cannot', () => {
+    const col = service.getColumns(authorId, projectId)[0];
+    // memberId(非管理者)はカラム削除不可
+    expect(() => service.deleteColumn(memberId, col.id)).toThrow(
+      ForbiddenError
+    );
+    // authorId(admin)は削除可
+    service.deleteColumn(authorId, col.id);
+    expect(() => service.updateColumn(authorId, col.id, { name: 'x' })).toThrow(
+      NotFoundError
+    );
+  });
+
+  it('clears startDate/tags/assigneeId via null on update', () => {
+    const col = service.getColumns(authorId, projectId)[0];
+    const item = service.createItem(authorId, projectId, {
+      title: 't',
+      columnId: col.id,
+      startDate: '2026-07-01',
+      tags: 'a,b',
+      assigneeId: memberId,
+    });
+    const cleared = service.updateItem(authorId, item.id, {
+      startDate: null,
+      tags: null,
+      assigneeId: null,
+    });
+    expect(cleared.startDate).toBeNull();
+    expect(cleared.tags).toBeNull();
+    expect(cleared.assigneeId).toBeNull();
+  });
 });