diff --git a/package.json b/package.json
index c8e65b8b4c..ce82682669 100644
--- a/package.json
+++ b/package.json
@@ -199,6 +199,7 @@
 		"recaptcha-promise": "0.1.3",
 		"reconnecting-websocket": "4.2.0",
 		"redis": "2.8.0",
+		"redis-lock": "0.1.4",
 		"reflect-metadata": "0.1.13",
 		"rename": "1.0.4",
 		"request": "2.88.0",
diff --git a/src/misc/app-lock.ts b/src/misc/app-lock.ts
new file mode 100644
index 0000000000..30579ed934
--- /dev/null
+++ b/src/misc/app-lock.ts
@@ -0,0 +1,22 @@
+import redis from '../db/redis';
+import { promisify } from 'util';
+
+/**
+ * Retry delay (ms) for lock acquisition
+ */
+const retryDelay = 100;
+
+const lock: (key: string, timeout?: number) => Promise<() => void>
+	= redis
+	? promisify(require('redis-lock')(redis, retryDelay))
+	: async () => () => { };
+
+/**
+ * Get AP Object lock
+ * @param uri AP object ID
+ * @param timeout Lock timeout (ms), The timeout releases previous lock.
+ * @returns Unlock function
+ */
+export function getApLock(uri: string, timeout = 30 * 1000) {
+	return lock(`ap-object:${uri}`, timeout);
+}
diff --git a/src/remote/activitypub/kernel/announce/note.ts b/src/remote/activitypub/kernel/announce/note.ts
index 2a07f50c8a..f0594a57b7 100644
--- a/src/remote/activitypub/kernel/announce/note.ts
+++ b/src/remote/activitypub/kernel/announce/note.ts
@@ -7,6 +7,7 @@ import { resolvePerson } from '../../models/person';
 import { apLogger } from '../../logger';
 import { extractDbHost } from '../../../../misc/convert-host';
 import { fetchMeta } from '../../../../misc/fetch-meta';
+import { getApLock } from '../../../../misc/app-lock';
 
 const logger = apLogger;
 
@@ -25,47 +26,53 @@ export default async function(resolver: Resolver, actor: IRemoteUser, activity:
 	const meta = await fetchMeta();
 	if (meta.blockedHosts.includes(extractDbHost(uri))) return;
 
-	// 既に同じURIを持つものが登録されていないかチェック
-	const exist = await fetchNote(uri);
-	if (exist) {
-		return;
-	}
+	const unlock = await getApLock(uri);
 
-	// Announce対象をresolve
-	let renote;
 	try {
-		renote = await resolveNote(note);
-	} catch (e) {
-		// 対象が4xxならスキップ
-		if (e.statusCode >= 400 && e.statusCode < 500) {
-			logger.warn(`Ignored announce target ${note.inReplyTo} - ${e.statusCode}`);
+		// 既に同じURIを持つものが登録されていないかチェック
+		const exist = await fetchNote(uri);
+		if (exist) {
 			return;
 		}
-		logger.warn(`Error in announce target ${note.inReplyTo} - ${e.statusCode || e}`);
-		throw e;
+
+		// Announce対象をresolve
+		let renote;
+		try {
+			renote = await resolveNote(note);
+		} catch (e) {
+			// 対象が4xxならスキップ
+			if (e.statusCode >= 400 && e.statusCode < 500) {
+				logger.warn(`Ignored announce target ${note.inReplyTo} - ${e.statusCode}`);
+				return;
+			}
+			logger.warn(`Error in announce target ${note.inReplyTo} - ${e.statusCode || e}`);
+			throw e;
+		}
+
+		logger.info(`Creating the (Re)Note: ${uri}`);
+
+		//#region Visibility
+		const to = getApIds(activity.to);
+		const cc = getApIds(activity.cc);
+
+		const visibility = getVisibility(to, cc, actor);
+
+		let visibleUsers: User[] = [];
+		if (visibility == 'specified') {
+			visibleUsers = await Promise.all(to.map(uri => resolvePerson(uri)));
+		}
+		//#endergion
+
+		await post(actor, {
+			createdAt: activity.published ? new Date(activity.published) : null,
+			renote,
+			visibility,
+			visibleUsers,
+			uri
+		});
+	} finally {
+		unlock();
 	}
-
-	logger.info(`Creating the (Re)Note: ${uri}`);
-
-	//#region Visibility
-	const to = getApIds(activity.to);
-	const cc = getApIds(activity.cc);
-
-	const visibility = getVisibility(to, cc, actor);
-
-	let visibleUsers: User[] = [];
-	if (visibility == 'specified') {
-		visibleUsers = await Promise.all(to.map(uri => resolvePerson(uri)));
-	}
-	//#endergion
-
-	await post(actor, {
-		createdAt: activity.published ? new Date(activity.published) : null,
-		renote,
-		visibility,
-		visibleUsers,
-		uri
-	});
 }
 
 type visibility = 'public' | 'home' | 'followers' | 'specified';
diff --git a/src/remote/activitypub/kernel/create/note.ts b/src/remote/activitypub/kernel/create/note.ts
index 70e61bdf1b..a28eaa11fb 100644
--- a/src/remote/activitypub/kernel/create/note.ts
+++ b/src/remote/activitypub/kernel/create/note.ts
@@ -1,13 +1,23 @@
 import Resolver from '../../resolver';
 import { IRemoteUser } from '../../../../models/entities/user';
 import { createNote, fetchNote } from '../../models/note';
+import { getApId } from '../../type';
+import { getApLock } from '../../../../misc/app-lock';
 
 /**
  * 投稿作成アクティビティを捌きます
  */
 export default async function(resolver: Resolver, actor: IRemoteUser, note: any, silent = false): Promise<void> {
-	const exist = await fetchNote(note);
-	if (exist == null) {
-		await createNote(note);
+	const uri = getApId(note);
+
+	const unlock = await getApLock(uri);
+
+	try {
+		const exist = await fetchNote(note);
+		if (exist == null) {
+			await createNote(note);
+		}
+	} finally {
+		unlock();
 	}
 }
diff --git a/src/remote/activitypub/models/note.ts b/src/remote/activitypub/models/note.ts
index 9afbb39151..6430813589 100644
--- a/src/remote/activitypub/models/note.ts
+++ b/src/remote/activitypub/models/note.ts
@@ -22,6 +22,7 @@ import { Emoji } from '../../../models/entities/emoji';
 import { genId } from '../../../misc/gen-id';
 import { fetchMeta } from '../../../misc/fetch-meta';
 import { ensure } from '../../../prelude/ensure';
+import { getApLock } from '../../../misc/app-lock';
 
 const logger = apLogger;
 
@@ -257,30 +258,24 @@ export async function resolveNote(value: string | IObject, resolver?: Resolver):
 	const meta = await fetchMeta();
 	if (meta.blockedHosts.includes(extractDbHost(uri))) throw { statusCode: 451 };
 
-	//#region このサーバーに既に登録されていたらそれを返す
-	const exist = await fetchNote(uri);
+	const unlock = await getApLock(uri);
 
-	if (exist) {
-		return exist;
-	}
-	//#endregion
+	try {
+		//#region このサーバーに既に登録されていたらそれを返す
+		const exist = await fetchNote(uri);
 
-	// リモートサーバーからフェッチしてきて登録
-	// ここでuriの代わりに添付されてきたNote Objectが指定されていると、サーバーフェッチを経ずにノートが生成されるが
-	// 添付されてきたNote Objectは偽装されている可能性があるため、常にuriを指定してサーバーフェッチを行う。
-	return await createNote(uri, resolver, true).catch(e => {
-		if (e.name === 'duplicated') {
-			return fetchNote(uri).then(note => {
-				if (note == null) {
-					throw new Error('something happened');
-				} else {
-					return note;
-				}
-			});
-		} else {
-			throw e;
+		if (exist) {
+			return exist;
 		}
-	});
+		//#endregion
+
+		// リモートサーバーからフェッチしてきて登録
+		// ここでuriの代わりに添付されてきたNote Objectが指定されていると、サーバーフェッチを経ずにノートが生成されるが
+		// 添付されてきたNote Objectは偽装されている可能性があるため、常にuriを指定してサーバーフェッチを行う。
+		return await createNote(uri, resolver, true);
+	} finally {
+		unlock();
+	}
 }
 
 export async function extractEmojis(tags: ITag[], host: string): Promise<Emoji[]> {
diff --git a/yarn.lock b/yarn.lock
index 1b20c58129..5481200849 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -9561,6 +9561,11 @@ redis-errors@^1.0.0, redis-errors@^1.2.0:
   resolved "https://registry.yarnpkg.com/redis-errors/-/redis-errors-1.2.0.tgz#eb62d2adb15e4eaf4610c04afe1529384250abad"
   integrity sha1-62LSrbFeTq9GEMBK/hUpOEJQq60=
 
+redis-lock@0.1.4:
+  version "0.1.4"
+  resolved "https://registry.yarnpkg.com/redis-lock/-/redis-lock-0.1.4.tgz#e83590bee22b5f01cdb65bfbd88d988045356272"
+  integrity sha512-7/+zu86XVQfJVx1nHTzux5reglDiyUCDwmW7TSlvVezfhH2YLc/Rc8NE0ejQG+8/0lwKzm29/u/4+ogKeLosiA==
+
 redis-parser@^2.6.0:
   version "2.6.0"
   resolved "https://registry.yarnpkg.com/redis-parser/-/redis-parser-2.6.0.tgz#52ed09dacac108f1a631c07e9b69941e7a19504b"