diff --git a/package.json b/package.json
index a4283c15bd..8948ce0bf1 100644
--- a/package.json
+++ b/package.json
@@ -30,6 +30,7 @@
     "@types/compression": "0.0.33",
     "@types/cors": "2.8.1",
     "@types/debug": "0.0.29",
+    "@types/deep-equal": "1.0.0",
     "@types/elasticsearch": "5.0.13",
     "@types/escape-html": "0.0.19",
     "@types/event-stream": "3.3.31",
@@ -78,6 +79,7 @@
     "crypto": "0.0.3",
     "css-loader": "0.27.3",
     "debug": "2.6.3",
+    "deep-equal": "1.0.1",
     "deepcopy": "0.6.3",
     "download": "5.0.3",
     "elasticsearch": "12.1.3",
diff --git a/src/api/endpoints/posts/create.ts b/src/api/endpoints/posts/create.ts
index 60b3592682..9ece143fa1 100644
--- a/src/api/endpoints/posts/create.ts
+++ b/src/api/endpoints/posts/create.ts
@@ -2,6 +2,7 @@
  * Module dependencies
  */
 import $ from 'cafy';
+import deepEqual = require('deep-equal');
 import parse from '../../common/text';
 import Post from '../../models/post';
 import { isValidText } from '../../models/post';
@@ -142,6 +143,20 @@ module.exports = (params, user, app) => new Promise(async (res, rej) => {
 		return rej('text, media_ids, repost_id or poll is required');
 	}
 
+	// 直近の投稿と重複してたらエラー
+	// TODO: 直近の投稿が一日前くらいなら重複とは見なさない
+	if (user.latest_post) {
+		if (deepEqual({
+			text: user.latest_post.text,
+			media_ids: (user.latest_post.media_ids || []).map(id => id.toString())
+		}, {
+			text: text,
+			media_ids: (files || []).map(file => file._id.toString())
+		})) {
+			return rej('duplicate');
+		}
+	}
+
 	// 投稿を作成
 	const post = await Post.insert({
 		created_at: new Date(),
@@ -163,6 +178,12 @@ module.exports = (params, user, app) => new Promise(async (res, rej) => {
 	//--------------------------------
 	// Post processes
 
+	User.update({ _id: user._id }, {
+		$set: {
+			latest_post: post
+		}
+	});
+
 	let mentions = [];
 
 	function addMention(mentionee, type) {
diff --git a/src/api/serializers/user.ts b/src/api/serializers/user.ts
index d367dc8657..bdbc749589 100644
--- a/src/api/serializers/user.ts
+++ b/src/api/serializers/user.ts
@@ -65,6 +65,9 @@ export default (
 	_user.id = _user._id;
 	delete _user._id;
 
+	// Remove needless properties
+	delete _user.lates_post;
+
 	// Remove private properties
 	delete _user.password;
 	delete _user.token;