diff --git a/CHANGELOG.md b/CHANGELOG.md
index b996216ac1..a7da62a4ad 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -118,6 +118,8 @@
 		サーバー管理者は各サーバーの必要に応じ`drive_file` `("uri")`に対するインデックスを張りなおすことでより安定しDBの探索が行われる可能性があります。詳細 は [GitHub](https://github.com/misskey-dev/misskey/pull/14323#issuecomment-2257562228)で確認可能です
 - Fix: 自分のフォロワー限定投稿に対するリプライがホームタイムラインで見えないことが有る問題を修正
 - Fix: フォローしていないユーザによるフォロワー限定投稿に対するリプライがソーシャルタイムラインで表示されることがある問題を修正
+- Fix: ActivityPubのエンティティタイプ判定で不明なタイプを受け取った場合でも処理を継続するように
+  - キュー処理のつまりが改善される可能性があります
 
 ### Misskey.js
 - Feat: `/drive/files/create` のリクエストに対応（`multipart/form-data`に対応）
diff --git a/packages/backend/src/core/activitypub/models/ApNoteService.ts b/packages/backend/src/core/activitypub/models/ApNoteService.ts
index 0766a8cd85..cc5addcf20 100644
--- a/packages/backend/src/core/activitypub/models/ApNoteService.ts
+++ b/packages/backend/src/core/activitypub/models/ApNoteService.ts
@@ -83,9 +83,10 @@ export class ApNoteService {
 	@bindThis
 	public validateNote(object: IObject, uri: string): Error | null {
 		const expectHost = this.utilityService.extractDbHost(uri);
+		const apType = getApType(object);
 
-		if (!validPost.includes(getApType(object))) {
-			return new IdentifiableError('d450b8a9-48e4-4dab-ae36-f4db763fda7c', `invalid Note: invalid object type ${getApType(object)}`);
+		if (apType == null || !validPost.includes(apType)) {
+			return new IdentifiableError('d450b8a9-48e4-4dab-ae36-f4db763fda7c', `invalid Note: invalid object type ${apType ?? 'undefined'}`);
 		}
 
 		if (object.id && this.utilityService.extractDbHost(object.id) !== expectHost) {
diff --git a/packages/backend/src/core/activitypub/type.ts b/packages/backend/src/core/activitypub/type.ts
index 8edd8a1aba..c92e2b805f 100644
--- a/packages/backend/src/core/activitypub/type.ts
+++ b/packages/backend/src/core/activitypub/type.ts
@@ -60,11 +60,14 @@ export function getApId(value: string | IObject): string {
 
 /**
  * Get ActivityStreams Object type
+ *
+ * タイプ判定ができなかった場合に、あえてエラーではなくnullを返すようにしている。
+ * 詳細: https://github.com/misskey-dev/misskey/issues/14239
  */
-export function getApType(value: IObject): string {
+export function getApType(value: IObject): string | null {
 	if (typeof value.type === 'string') return value.type;
 	if (Array.isArray(value.type) && typeof value.type[0] === 'string') return value.type[0];
-	throw new Error('cannot detect type');
+	return null;
 }
 
 export function getOneApHrefNullable(value: ApObject | undefined): string | undefined {
@@ -108,8 +111,10 @@ export interface IOrderedCollection extends IObject {
 
 export const validPost = ['Note', 'Question', 'Article', 'Audio', 'Document', 'Image', 'Page', 'Video', 'Event'];
 
-export const isPost = (object: IObject): object is IPost =>
-	validPost.includes(getApType(object));
+export const isPost = (object: IObject): object is IPost => {
+	const type = getApType(object);
+	return type != null && validPost.includes(type);
+};
 
 export interface IPost extends IObject {
 	type: 'Note' | 'Question' | 'Article' | 'Audio' | 'Document' | 'Image' | 'Page' | 'Video' | 'Event';
@@ -159,8 +164,10 @@ export const isTombstone = (object: IObject): object is ITombstone =>
 
 export const validActor = ['Person', 'Service', 'Group', 'Organization', 'Application'];
 
-export const isActor = (object: IObject): object is IActor =>
-	validActor.includes(getApType(object));
+export const isActor = (object: IObject): object is IActor => {
+	const type = getApType(object);
+	return type != null && validActor.includes(type);
+};
 
 export interface IActor extends IObject {
 	type: 'Person' | 'Service' | 'Organization' | 'Group' | 'Application';
@@ -246,12 +253,16 @@ export interface IKey extends IObject {
 	publicKeyPem: string | Buffer;
 }
 
+export const validDocumentTypes = ['Audio', 'Document', 'Image', 'Page', 'Video'];
+
 export interface IApDocument extends IObject {
 	type: 'Audio' | 'Document' | 'Image' | 'Page' | 'Video';
 }
 
-export const isDocument = (object: IObject): object is IApDocument =>
-	['Audio', 'Document', 'Image', 'Page', 'Video'].includes(getApType(object));
+export const isDocument = (object: IObject): object is IApDocument => {
+	const type = getApType(object);
+	return type != null && validDocumentTypes.includes(type);
+};
 
 export interface IApImage extends IApDocument {
 	type: 'Image';
@@ -329,7 +340,10 @@ export const isAccept = (object: IObject): object is IAccept => getApType(object
 export const isReject = (object: IObject): object is IReject => getApType(object) === 'Reject';
 export const isAdd = (object: IObject): object is IAdd => getApType(object) === 'Add';
 export const isRemove = (object: IObject): object is IRemove => getApType(object) === 'Remove';
-export const isLike = (object: IObject): object is ILike => getApType(object) === 'Like' || getApType(object) === 'EmojiReaction' || getApType(object) === 'EmojiReact';
+export const isLike = (object: IObject): object is ILike => {
+	const type = getApType(object);
+	return type != null && ['Like', 'EmojiReaction', 'EmojiReact'].includes(type);
+};
 export const isAnnounce = (object: IObject): object is IAnnounce => getApType(object) === 'Announce';
 export const isBlock = (object: IObject): object is IBlock => getApType(object) === 'Block';
 export const isFlag = (object: IObject): object is IFlag => getApType(object) === 'Flag';