diff --git a/packages/backend/src/server/activitypub.ts b/packages/backend/src/server/activitypub.ts
index 21be0a251..f2d320bb6 100644
--- a/packages/backend/src/server/activitypub.ts
+++ b/packages/backend/src/server/activitypub.ts
@@ -18,6 +18,7 @@ import { ILocalUser, User } from '@/models/entities/user.js';
 import { In } from 'typeorm';
 import { renderLike } from '@/remote/activitypub/renderer/like.js';
 import { getUserKeypair } from '@/misc/keypair-store.js';
+import { noteCache, userCache } from './activitypub/cache.js';
 
 // Init router
 const router = new Router();
@@ -65,11 +66,12 @@ router.post('/users/:user/inbox', json(), inbox);
 router.get('/notes/:note', async (ctx, next) => {
 	if (!isActivityPubReq(ctx)) return await next();
 
-	const note = await Notes.findOne({
+	// TODO: typeorm 3.0にしたら .then(x => x || null) は消せる
+	const note = await noteCache.fetch(ctx.params.note, () => Notes.findOne({
 		id: ctx.params.note,
 		visibility: In(['public' as const, 'home' as const]),
 		localOnly: false,
-	});
+	}).then(x => x || null));
 
 	if (note == null) {
 		ctx.status = 404;
@@ -148,7 +150,7 @@ router.get('/users/:user/publickey', async ctx => {
 });
 
 // user
-async function userInfo(ctx: Router.RouterContext, user: User | undefined) {
+async function userInfo(ctx: Router.RouterContext, user: User | undefined | null) {
 	if (user == null) {
 		ctx.status = 404;
 		return;
@@ -164,11 +166,12 @@ router.get('/users/:user', async (ctx, next) => {
 
 	const userId = ctx.params.user;
 
-	const user = await Users.findOne({
+	// TODO: typeorm 3.0にしたら .then(x => x || null) は消せる
+	const user = await userCache.fetch(userId, () => Users.findOne({
 		id: userId,
 		host: null,
 		isSuspended: false,
-	});
+	}).then(x => x || null));
 
 	await userInfo(ctx, user);
 });
diff --git a/packages/backend/src/server/activitypub/cache.ts b/packages/backend/src/server/activitypub/cache.ts
new file mode 100644
index 000000000..4ebec77dc
--- /dev/null
+++ b/packages/backend/src/server/activitypub/cache.ts
@@ -0,0 +1,6 @@
+import { Cache } from "@/misc/cache";
+import { Note } from "@/models/entities/note";
+import { User } from "@/models/entities/user";
+
+export const userCache = new Cache<User | null>(1000 * 60 * 30);
+export const noteCache = new Cache<Note | null>(1000 * 60 * 30);
diff --git a/packages/backend/src/server/activitypub/featured.ts b/packages/backend/src/server/activitypub/featured.ts
index 129881a71..d06a28a9c 100644
--- a/packages/backend/src/server/activitypub/featured.ts
+++ b/packages/backend/src/server/activitypub/featured.ts
@@ -5,15 +5,16 @@ import renderOrderedCollection from '@/remote/activitypub/renderer/ordered-colle
 import { setResponseType } from '../activitypub.js';
 import renderNote from '@/remote/activitypub/renderer/note.js';
 import { Users, Notes, UserNotePinings } from '@/models/index.js';
+import { userCache } from './cache.js';
 
 export default async (ctx: Router.RouterContext) => {
 	const userId = ctx.params.user;
 
-	// Verify user
-	const user = await Users.findOne({
+	// TODO: typeorm 3.0にしたら .then(x => x || null) は消せる
+	const user = await userCache.fetch(userId, () => Users.findOne({
 		id: userId,
 		host: null,
-	});
+	}).then(x => x || null));
 
 	if (user == null) {
 		ctx.status = 404;
diff --git a/packages/backend/src/server/activitypub/followers.ts b/packages/backend/src/server/activitypub/followers.ts
index 5d1d7c59e..fdae9dd92 100644
--- a/packages/backend/src/server/activitypub/followers.ts
+++ b/packages/backend/src/server/activitypub/followers.ts
@@ -10,6 +10,7 @@ import renderFollowUser from '@/remote/activitypub/renderer/follow-user.js';
 import { setResponseType } from '../activitypub.js';
 import { Users, Followings, UserProfiles } from '@/models/index.js';
 import { LessThan } from 'typeorm';
+import { userCache } from './cache.js';
 
 export default async (ctx: Router.RouterContext) => {
 	const userId = ctx.params.user;
@@ -27,11 +28,11 @@ export default async (ctx: Router.RouterContext) => {
 		return;
 	}
 
-	// Verify user
-	const user = await Users.findOne({
+	// TODO: typeorm 3.0にしたら .then(x => x || null) は消せる
+	const user = await userCache.fetch(userId, () => Users.findOne({
 		id: userId,
 		host: null,
-	});
+	}).then(x => x || null));
 
 	if (user == null) {
 		ctx.status = 404;
diff --git a/packages/backend/src/server/activitypub/following.ts b/packages/backend/src/server/activitypub/following.ts
index 23110ce87..eb1b7a9d8 100644
--- a/packages/backend/src/server/activitypub/following.ts
+++ b/packages/backend/src/server/activitypub/following.ts
@@ -11,6 +11,7 @@ import { setResponseType } from '../activitypub.js';
 import { Users, Followings, UserProfiles } from '@/models/index.js';
 import { LessThan, FindConditions } from 'typeorm';
 import { Following } from '@/models/entities/following.js';
+import { userCache } from './cache.js';
 
 export default async (ctx: Router.RouterContext) => {
 	const userId = ctx.params.user;
@@ -28,11 +29,11 @@ export default async (ctx: Router.RouterContext) => {
 		return;
 	}
 
-	// Verify user
-	const user = await Users.findOne({
+	// TODO: typeorm 3.0にしたら .then(x => x || null) は消せる
+	const user = await userCache.fetch(userId, () => Users.findOne({
 		id: userId,
 		host: null,
-	});
+	}).then(x => x || null));
 
 	if (user == null) {
 		ctx.status = 404;
diff --git a/packages/backend/src/server/activitypub/outbox.ts b/packages/backend/src/server/activitypub/outbox.ts
index 57c126752..db2a18efc 100644
--- a/packages/backend/src/server/activitypub/outbox.ts
+++ b/packages/backend/src/server/activitypub/outbox.ts
@@ -15,6 +15,7 @@ import { Users, Notes } from '@/models/index.js';
 import { makePaginationQuery } from '../api/common/make-pagination-query.js';
 import { Brackets } from 'typeorm';
 import { Note } from '@/models/entities/note.js';
+import { userCache } from './cache.js';
 
 export default async (ctx: Router.RouterContext) => {
 	const userId = ctx.params.user;
@@ -35,11 +36,11 @@ export default async (ctx: Router.RouterContext) => {
 		return;
 	}
 
-	// Verify user
-	const user = await Users.findOne({
+	// TODO: typeorm 3.0にしたら .then(x => x || null) は消せる
+	const user = await userCache.fetch(userId, () => Users.findOne({
 		id: userId,
 		host: null,
-	});
+	}).then(x => x || null));
 
 	if (user == null) {
 		ctx.status = 404;