diff --git a/app/_locales/ja/messages.json b/app/_locales/ja/messages.json
index fe2f2fc..b464a45 100644
--- a/app/_locales/ja/messages.json
+++ b/app/_locales/ja/messages.json
@@ -75,6 +75,9 @@
   "wentWrong": {
     "message": "申し訳ございません。問題が発生しました。"
   },
+  "confirmPublishOverwrite": {
+    "message": "小説の入力内容が変更されています。\n上書きしてもよろしいですか？"
+  },
 
   "options": {
     "message": "設定"
diff --git a/app/scripts/lib/sites/kakuyomu/publish.js b/app/scripts/lib/sites/kakuyomu/publish.js
index cdbfadf..4abbf96 100644
--- a/app/scripts/lib/sites/kakuyomu/publish.js
+++ b/app/scripts/lib/sites/kakuyomu/publish.js
@@ -1,4 +1,5 @@
 import _ from "lodash";
+import { translate } from "@io-monad/chrome-util";
 import moment from "../../util/moment";
 import openPage from "../../util/open-page";
 import KakuyomuURL from "./url";
@@ -12,7 +13,7 @@ import KakuyomuURL from "./url";
 export default function publish(publication) {
   const url = getURL(publication);
   const code = getCode(publication);
-  return openPage(url, code);
+  return openPage(url, code, { update: true });
 }
 
 function getURL(pub) {
@@ -24,31 +25,44 @@ function getURL(pub) {
 }
 
 function getCode(pub) {
-  const title = JSON.stringify(pub.title || "");
-  const body = JSON.stringify(pub.body || "");
-  let code = `
+  const embedPub = {
+    title: pub.title || "",
+    body: pub.body || "",
+  };
+  if (pub.time) {
+    const time = moment(pub.time).tz("Asia/Tokyo");
+    embedPub.date = time.format("YYYY-MM-DD");
+    embedPub.time = time.format("HH:mm");
+  }
+  return `
+    var pub = ${JSON.stringify(embedPub)};
     var form = document.getElementById("episode-editForm");
 
+    var lastPub = window.novelousLastPublication || { title: "", body: "" };
+    if (form.title.value !== lastPub.title || form.body.value !== lastPub.body) {
+      if (!confirm(${JSON.stringify(translate("confirmPublishOverwrite"))})) {
+        return;
+      }
+    }
+
     var change = document.createEvent("HTMLEvents");
     change.initEvent("change", true, true);
 
-    form.title.value = ${title};
+    form.title.value = pub.title;
     form.title.dispatchEvent(change);
-    form.body.value = ${body};
+    form.body.value = pub.body;
     form.body.dispatchEvent(change);
-  `;
 
-  if (pub.time) {
-    const time = moment(pub.time).tz("Asia/Tokyo");
-    const dateValue = JSON.stringify(time.format("YYYY-MM-DD"));
-    const timeValue = JSON.stringify(time.format("HH:mm"));
-    code += `
-      document.querySelector(".js-reservation-panel-button").click();
+    if (pub.date && pub.time) {
+      var button = document.querySelector(".js-reservation-panel-button");
+      if (!/isPanelShown/.test(button.className)) {
+        button.click();
+      }
       document.getElementById("reservationInput-reserved").click();
-      form.reservation_date.value = ${dateValue};
-      form.reservation_time.value = ${timeValue};
-    `;
-  }
+      form.reservation_date.value = pub.date;
+      form.reservation_time.value = pub.time;
+    }
 
-  return code;
+    window.novelousLastPublication = pub;
+  `;
 }
diff --git a/app/scripts/lib/sites/narou/publish.js b/app/scripts/lib/sites/narou/publish.js
index 2a77e3a..380734a 100644
--- a/app/scripts/lib/sites/narou/publish.js
+++ b/app/scripts/lib/sites/narou/publish.js
@@ -1,4 +1,5 @@
 import _ from "lodash";
+import { translate } from "@io-monad/chrome-util";
 import moment from "../../util/moment";
 import openPage from "../../util/open-page";
 import NarouURL from "./url";
@@ -12,7 +13,7 @@ import NarouURL from "./url";
 export default function publish(publication) {
   const url = getURL(publication);
   const code = getCode(publication);
-  return openPage(url, code);
+  return openPage(url, code, { update: true });
 }
 
 function getURL(pub) {
@@ -24,25 +25,36 @@ function getURL(pub) {
 }
 
 function getCode(pub) {
-  const title = JSON.stringify(pub.title || "");
-  const body = JSON.stringify(pub.body || "");
-  let code = `
-    var form = document.getElementById("manage_form");
-    form.subtitle.value = ${title};
-    form.novel.value = ${body};
-  `;
-
+  const embedPub = {
+    title: pub.title || "",
+    body: pub.body || "",
+  };
   if (pub.time) {
     const time = moment(pub.time).tz("Asia/Tokyo");
-    const monthValue = JSON.stringify(time.format("YYYY-MM"));
-    const dayValue = JSON.stringify(time.format("D"));
-    const hourValue = JSON.stringify(time.format("H"));
-    code += `
-      form.month.value = ${monthValue};
-      form.day.value = ${dayValue};
-      form.hour.value = ${hourValue};
-    `;
+    embedPub.month = time.format("YYYY-MM");
+    embedPub.day = time.format("D");
+    embedPub.hour = time.format("H");
   }
+  return `
+    var pub = ${JSON.stringify(embedPub)};
+    var form = document.getElementById("manage_form");
 
-  return code;
+    var lastPub = window.novelousLastPublication || { title: "", body: "" };
+    if (form.subtitle.value !== lastPub.title || form.novel.value !== lastPub.body) {
+      if (!confirm(${JSON.stringify(translate("confirmPublishOverwrite"))})) {
+        return;
+      }
+    }
+
+    form.subtitle.value = pub.title;
+    form.novel.value = pub.body;
+
+    if (pub.month && pub.day) {
+      form.month.value = pub.month;
+      form.day.value = pub.day;
+      form.hour.value = pub.hour;
+    }
+
+    window.novelousLastPublication = pub;
+  `;
 }
diff --git a/app/scripts/lib/util/open-page.js b/app/scripts/lib/util/open-page.js
index a2cab03..930e800 100644
--- a/app/scripts/lib/util/open-page.js
+++ b/app/scripts/lib/util/open-page.js
@@ -3,20 +3,49 @@
  *
  * @param {string} url - A URL of the opening page.
  * @param {string} code - A code to be executed on the page.
+ * @param {Object} [options] - Options.
+ * @param {boolean} [options.update=false] - Set this to `true` for updating existing tab.
  * @return {Promise}
  */
-export default function openPage(url, code) {
-  return new Promise((resolve, reject) => {
-    chrome.tabs.create({ url }, (tab) => {
-      const wrapped = wrapInjectCode(code);
-      chrome.tabs.executeScript(tab.id, { code: wrapped }, (results) => {
-        // results = [error] or [null]
-        if (results.length > 0 && results[0]) {
-          reject(results[0]);
+export default function openPage(url, code, options) {
+  options = options || {};
+  return new Promise(resolve => {
+    if (options.update) {
+      chrome.tabs.query({ url }, (tabs) => {
+        if (tabs.length > 0) {
+          chrome.tabs.update(tabs[0].id, { active: true }, tab => {
+            resolve(executeCode(tab, code));
+          });
         } else {
-          resolve();
+          chrome.tabs.create({ url }, tab => {
+            resolve(executeCode(tab, code));
+          });
         }
       });
+    } else {
+      chrome.tabs.create({ url }, tab => {
+        resolve(executeCode(tab, code));
+      });
+    }
+  });
+}
+
+/**
+ * @param {chrome~Tab} tab
+ * @param {string} code
+ * @return {Promise}
+ * @private
+ */
+function executeCode(tab, code) {
+  return new Promise((resolve, reject) => {
+    const wrapped = wrapInjectCode(code);
+    chrome.tabs.executeScript(tab.id, { code: wrapped }, (results) => {
+      // results = [error] or [null]
+      if (results.length > 0 && results[0]) {
+        reject(results[0]);
+      } else {
+        resolve();
+      }
     });
   });
 }
@@ -35,6 +64,6 @@ function wrapInjectCode(code) {
         return e.message || e;
       }
       return null;
-    })();
+    }());
   `;
 }
diff --git a/test/lib/sites/kakuyomu/publish-test.js b/test/lib/sites/kakuyomu/publish-test.js
index 784b5ae..9a18773 100644
--- a/test/lib/sites/kakuyomu/publish-test.js
+++ b/test/lib/sites/kakuyomu/publish-test.js
@@ -2,34 +2,69 @@ import { _, assert, factory } from "../../../common";
 import publish from "../../../../app/scripts/lib/sites/kakuyomu/publish";
 
 describe("KakuyomuPublish", () => {
-  it("publishes novel to sites", () => {
-    const pub = factory.buildSync("publication", {
+  let pub;
+  let publishUrl;
+  before(() => {
+    pub = factory.buildSync("publication", {
       sites: {
         kakuyomu: { novelId: "12341234" },
       },
     });
-    chrome.tabs.create.callsArgWithAsync(1, { id: 123 });
-    chrome.tabs.executeScript.callsArgWithAsync(2, [null]);
+    publishUrl = `https://kakuyomu.jp/my/works/${pub.sites.kakuyomu.novelId}/episodes/new`;
+  });
+
+  it("opens a new tab with publication contents", () => {
+    chrome.tabs.query.yieldsAsync([]);
+    chrome.tabs.create.yieldsAsync({ id: 123 });
+    chrome.tabs.executeScript.yieldsAsync([null]);
 
     return publish(pub).then(() => {
-      assert(chrome.tabs.create.calledOnce);
-      assert.deepEqual(chrome.tabs.create.args[0][0], {
-        url: `https://kakuyomu.jp/my/works/${pub.sites.kakuyomu.novelId}/episodes/new`,
+      assert(chrome.tabs.query.calledOnce === true);
+      assert.deepEqual(chrome.tabs.query.args[0][0], { url: publishUrl });
+
+      assert(chrome.tabs.create.calledOnce === true);
+      assert.deepEqual(chrome.tabs.create.args[0][0], { url: publishUrl });
+
+      assert(chrome.tabs.executeScript.calledOnce === true);
+      assert(chrome.tabs.executeScript.args[0][0] === 123);
+      assert(_.isString(chrome.tabs.executeScript.args[0][1].code));
+
+      const code = chrome.tabs.executeScript.args[0][1].code;
+      const embedPub = JSON.parse(code.match(/var pub = (.+?);/)[1]);
+      assert.deepEqual(embedPub, {
+        title: pub.title,
+        body: pub.body,
+        date: "2016-03-01",
+        time: "11:34",
       });
-      assert(chrome.tabs.executeScript.calledOnce);
+    });
+  });
+
+  it("updates an existing tab with publication contents", () => {
+    chrome.tabs.query.yieldsAsync([{ id: 123 }]);
+    chrome.tabs.update.yieldsAsync({ id: 123 });
+    chrome.tabs.executeScript.yieldsAsync([null]);
+
+    return publish(pub).then(() => {
+      assert(chrome.tabs.query.calledOnce === true);
+      assert.deepEqual(chrome.tabs.query.args[0][0], { url: publishUrl });
+
+      assert(chrome.tabs.update.calledOnce === true);
+      assert(chrome.tabs.update.args[0][0] === 123);
+      assert.deepEqual(chrome.tabs.update.args[0][1], { active: true });
+
+      assert(chrome.tabs.executeScript.calledOnce === true);
       assert(chrome.tabs.executeScript.args[0][0] === 123);
       assert(_.isString(chrome.tabs.executeScript.args[0][1].code));
 
       const code = chrome.tabs.executeScript.args[0][1].code;
-      const formValue = (name) => {
-        const re = new RegExp(`form\\.${name}\\.value = (.+?);`);
-        return JSON.parse(code.match(re)[1]);
-      };
-
-      assert(formValue("title") === pub.title);
-      assert(formValue("body") === pub.body);
-      assert(formValue("reservation_date") === "2016-03-01");
-      assert(formValue("reservation_time") === "11:34");
+      const embedPub = JSON.parse(code.match(/var pub = (.+?);/)[1]);
+      assert.deepEqual(embedPub, {
+        title: pub.title,
+        body: pub.body,
+        date: "2016-03-01",
+        time: "11:34",
+      });
     });
   });
 });
diff --git a/test/lib/sites/narou/publish-test.js b/test/lib/sites/narou/publish-test.js
index 6da9ece..5f6a3f3 100644
--- a/test/lib/sites/narou/publish-test.js
+++ b/test/lib/sites/narou/publish-test.js
@@ -2,31 +2,67 @@ import { _, assert, factory } from "../../../common";
 import publish from "../../../../app/scripts/lib/sites/narou/publish";
 
 describe("NarouPublish", () => {
-  it("publishes novel to sites", () => {
-    const pub = factory.buildSync("publication");
-    chrome.tabs.create.callsArgWithAsync(1, { id: 123 });
-    chrome.tabs.executeScript.callsArgWithAsync(2, [null]);
+  let pub;
+  let publishUrl;
+  before(() => {
+    pub = factory.buildSync("publication");
+    publishUrl = `http://syosetu.com/usernovelmanage/ziwainput/ncode/${pub.sites.narou.novelId}/`;
+  });
+
+  it("opens a new tab with publication contents", () => {
+    chrome.tabs.query.yieldsAsync([]);
+    chrome.tabs.create.yieldsAsync({ id: 123 });
+    chrome.tabs.executeScript.yieldsAsync([null]);
 
     return publish(pub).then(() => {
-      assert(chrome.tabs.create.calledOnce);
-      assert.deepEqual(chrome.tabs.create.args[0][0], {
-        url: `http://syosetu.com/usernovelmanage/ziwainput/ncode/${pub.sites.narou.novelId}/`,
+      assert(chrome.tabs.query.calledOnce === true);
+      assert.deepEqual(chrome.tabs.query.args[0][0], { url: publishUrl });
+
+      assert(chrome.tabs.create.calledOnce === true);
+      assert.deepEqual(chrome.tabs.create.args[0][0], { url: publishUrl });
+
+      assert(chrome.tabs.executeScript.calledOnce === true);
+      assert(chrome.tabs.executeScript.args[0][0] === 123);
+      assert(_.isString(chrome.tabs.executeScript.args[0][1].code));
+
+      const code = chrome.tabs.executeScript.args[0][1].code;
+      const embedPub = JSON.parse(code.match(/var pub = (.+?);/)[1]);
+      assert.deepEqual(embedPub, {
+        title: pub.title,
+        body: pub.body,
+        month: "2016-03",
+        day: "1",
+        hour: "11",
       });
-      assert(chrome.tabs.executeScript.calledOnce);
+    });
+  });
+
+  it("updates an existing tab with publication contents", () => {
+    chrome.tabs.query.yieldsAsync([{ id: 123 }]);
+    chrome.tabs.update.yieldsAsync({ id: 123 });
+    chrome.tabs.executeScript.yieldsAsync([null]);
+
+    return publish(pub).then(() => {
+      assert(chrome.tabs.query.calledOnce === true);
+      assert.deepEqual(chrome.tabs.query.args[0][0], { url: publishUrl });
+
+      assert(chrome.tabs.update.calledOnce === true);
+      assert(chrome.tabs.update.args[0][0] === 123);
+      assert.deepEqual(chrome.tabs.update.args[0][1], { active: true });
+
+      assert(chrome.tabs.executeScript.calledOnce === true);
       assert(chrome.tabs.executeScript.args[0][0] === 123);
       assert(_.isString(chrome.tabs.executeScript.args[0][1].code));
 
       const code = chrome.tabs.executeScript.args[0][1].code;
-      const formValue = (name) => {
-        const re = new RegExp(`form\\.${name}\\.value = (.+?);`);
-        return JSON.parse(code.match(re)[1]);
-      };
-
-      assert(formValue("subtitle") === pub.title);
-      assert(formValue("novel") === pub.body);
-      assert(formValue("month") === "2016-03");
-      assert(formValue("day") === "1");
-      assert(formValue("hour") === "11");
+      const embedPub = JSON.parse(code.match(/var pub = (.+?);/)[1]);
+      assert.deepEqual(embedPub, {
+        title: pub.title,
+        body: pub.body,
+        month: "2016-03",
+        day: "1",
+        hour: "11",
+      });
     });
   });
 });