diff --git a/server/hocuspocus/src/extractPlainTextFromYXml.test.ts b/server/hocuspocus/src/extractPlainTextFromYXml.test.ts
index edac4134..80dbf313 100644
--- a/server/hocuspocus/src/extractPlainTextFromYXml.test.ts
+++ b/server/hocuspocus/src/extractPlainTextFromYXml.test.ts
@@ -3,6 +3,25 @@ import * as Y from "yjs";
 import { buildContentPreview, extractTextFromYXml } from "./extractPlainTextFromYXml.js";
 
 describe("extractTextFromYXml", () => {
+  it("returns empty string for an empty fragment / 空の fragment では空文字を返す", () => {
+    const doc = new Y.Doc();
+    const fragment = doc.getXmlFragment("default");
+    expect(extractTextFromYXml(fragment)).toBe("");
+  });
+
+  it("extracts plain text from a simple paragraph / 単純なパラグラフからテキストを抽出する", () => {
+    const doc = new Y.Doc();
+    doc.transact(() => {
+      const fragment = doc.getXmlFragment("default");
+      const p = new Y.XmlElement("paragraph");
+      fragment.push([p]);
+      const t = new Y.XmlText();
+      t.insert(0, "Hello world");
+      p.push([t]);
+    });
+    expect(extractTextFromYXml(doc.getXmlFragment("default")).trim()).toBe("Hello world");
+  });
+
   it("does not insert a newline inside a paragraph between inline bold and following text", () => {
     const doc = new Y.Doc();
     doc.transact(() => {
@@ -49,6 +68,70 @@ describe("extractTextFromYXml", () => {
     expect(plain.includes("First") && plain.includes("Second")).toBe(true);
     expect(/\n/.test(plain)).toBe(true);
   });
+
+  it("strips formatting attributes from XmlText delta (Tiptap marks) / XmlText の書式属性を除去する", () => {
+    const doc = new Y.Doc();
+    doc.transact(() => {
+      const fragment = doc.getXmlFragment("default");
+      const p = new Y.XmlElement("paragraph");
+      fragment.push([p]);
+      const t = new Y.XmlText();
+      t.insert(0, "Hello ");
+      t.insert(6, "world", { bold: true });
+      t.insert(11, "!");
+      p.push([t]);
+    });
+    const plain = extractTextFromYXml(doc.getXmlFragment("default")).trim();
+    expect(plain).toBe("Hello world!");
+    expect(plain).not.toContain("<bold>");
+    expect(plain).not.toContain("</bold>");
+  });
+
+  it("strips italic and other mark attributes / italic 等の書式属性も除去する", () => {
+    const doc = new Y.Doc();
+    doc.transact(() => {
+      const fragment = doc.getXmlFragment("default");
+      const p = new Y.XmlElement("paragraph");
+      fragment.push([p]);
+      const t = new Y.XmlText();
+      t.insert(0, "normal ");
+      t.insert(7, "italic", { italic: true });
+      t.insert(13, " ");
+      t.insert(14, "bold-italic", { bold: true, italic: true });
+      p.push([t]);
+    });
+    const plain = extractTextFromYXml(doc.getXmlFragment("default")).trim();
+    expect(plain).toBe("normal italic bold-italic");
+    expect(plain).not.toContain("<italic>");
+    expect(plain).not.toContain("<bold>");
+  });
+
+  it("handles nested elements (e.g. list items) / ネストされた要素を処理する", () => {
+    const doc = new Y.Doc();
+    doc.transact(() => {
+      const fragment = doc.getXmlFragment("default");
+      const list = new Y.XmlElement("bulletList");
+      const item1 = new Y.XmlElement("listItem");
+      const p1 = new Y.XmlElement("paragraph");
+      const t1 = new Y.XmlText();
+      t1.insert(0, "Item 1");
+      p1.push([t1]);
+      item1.push([p1]);
+
+      const item2 = new Y.XmlElement("listItem");
+      const p2 = new Y.XmlElement("paragraph");
+      const t2 = new Y.XmlText();
+      t2.insert(0, "Item 2");
+      p2.push([t2]);
+      item2.push([p2]);
+
+      list.push([item1, item2]);
+      fragment.push([list]);
+    });
+    const plain = extractTextFromYXml(doc.getXmlFragment("default"));
+    expect(plain).toContain("Item 1");
+    expect(plain).toContain("Item 2");
+  });
 });
 
 describe("buildContentPreview", () => {
diff --git a/server/hocuspocus/src/extractPlainTextFromYXml.ts b/server/hocuspocus/src/extractPlainTextFromYXml.ts
index 06ae89ca..8ac6fd31 100644
--- a/server/hocuspocus/src/extractPlainTextFromYXml.ts
+++ b/server/hocuspocus/src/extractPlainTextFromYXml.ts
@@ -30,7 +30,12 @@ function isInlineXmlElement(node: Y.XmlElement): boolean {
 
 /**
  * Y.Doc の XmlFragment（または XmlElement 根）からプレーンテキストを再帰的に抽出する。
+ * `Y.XmlText.toString()` / `toJSON()` は `<bold>` 等の HTML タグを返すため、
+ * `toDelta()` を使い `insert` 文字列のみを連結する。
+ *
  * Recursively extract plain text from a Y.XmlFragment or Y.XmlElement subtree.
+ * Uses `toDelta()` instead of `toString()` / `toJSON()` because the latter
+ * returns HTML-like tags (`<bold>`, `<italic>`, etc.) for formatted text.
  */
 export function extractTextFromYXml(node: Y.XmlFragment | Y.XmlElement): string {
   let text = "";
@@ -38,7 +43,13 @@ export function extractTextFromYXml(node: Y.XmlFragment | Y.XmlElement): string
   for (let i = 0; i < node.length; i++) {
     const child = node.get(i);
     if (child instanceof Y.XmlText) {
-      text += child.toString();
+      // toDelta() を使い書式属性なしの純粋なテキストのみを抽出する。
+      // Use toDelta() to extract pure text without formatting attributes.
+      for (const op of child.toDelta()) {
+        if (typeof op.insert === "string") {
+          text += op.insert;
+        }
+      }
     } else if (child instanceof Y.XmlElement) {
       const inner = extractTextFromYXml(child);
       const suffix = isInlineXmlElement(child) ? " " : "\n";
diff --git a/server/hocuspocus/src/index.ts b/server/hocuspocus/src/index.ts
index 03c8e6ac..a635ce5c 100644
--- a/server/hocuspocus/src/index.ts
+++ b/server/hocuspocus/src/index.ts
@@ -196,6 +196,8 @@ async function loadDocumentFromDb(pageId: string): Promise<Y.Doc> {
 
 async function saveDocumentToDb(pageId: string, document: Y.Doc): Promise<void> {
   const encodedState = Buffer.from(Y.encodeStateAsUpdate(document));
+  // Y.Doc からプレーンテキストを抽出（HTML タグなし・toDelta() ベース）
+  // Extract plain text from Y.Doc (without HTML tags, using toDelta())
   const contentText = extractTextFromYXml(document.getXmlFragment("default"));
   const contentPreview = buildContentPreview(contentText);
   const client = await getPool().connect();
@@ -207,8 +209,8 @@ async function saveDocumentToDb(pageId: string, document: Y.Doc): Promise<void>
         VALUES ($1, $2, 1, $3, NOW())
         ON CONFLICT (page_id) DO UPDATE
           SET ydoc_state = EXCLUDED.ydoc_state,
-              version = page_contents.version + 1,
               content_text = EXCLUDED.content_text,
+              version = page_contents.version + 1,
               updated_at = NOW()
       `,
       [pageId, encodedState, contentText],
diff --git a/src/lib/collaboration/CollaborationManager.ts b/src/lib/collaboration/CollaborationManager.ts
index 7b8d51ef..b7f7dcc7 100644
--- a/src/lib/collaboration/CollaborationManager.ts
+++ b/src/lib/collaboration/CollaborationManager.ts
@@ -296,7 +296,15 @@ export class CollaborationManager {
     const parts: string[] = [];
     const walk = (node: Y.XmlFragment | Y.XmlElement | Y.XmlText) => {
       if (node instanceof Y.XmlText) {
-        parts.push(node.toJSON());
+        // toDelta() を使い書式属性なしの純粋なテキストのみを抽出する。
+        // toString() / toJSON() は <bold> 等の HTML タグを返すため使用しない。
+        // Use toDelta() to extract pure text without formatting attributes.
+        // toString() / toJSON() return HTML-like tags (<bold>, etc.) so we avoid them.
+        for (const op of node.toDelta()) {
+          if (typeof op.insert === "string") {
+            parts.push(op.insert);
+          }
+        }
       } else {
         for (const child of node.toArray()) {
           if (