diff --git a/browser/components/MarkdownPreview.js b/browser/components/MarkdownPreview.js
index 460920d8..d744a2e7 100644
--- a/browser/components/MarkdownPreview.js
+++ b/browser/components/MarkdownPreview.js
@@ -8,21 +8,7 @@ import flowchart from 'flowchart'
 import SequenceDiagram from 'js-sequence-diagrams'
 import eventEmitter from 'browser/main/lib/eventEmitter'
 import fs from 'fs'
-
-function decodeHTMLEntities (text) {
-  var entities = [
-    ['apos', '\''],
-    ['amp', '&'],
-    ['lt', '<'],
-    ['gt', '>']
-  ]
-
-  for (var i = 0, max = entities.length; i < max; ++i) {
-    text = text.replace(new RegExp('&' + entities[i][0] + ';', 'g'), entities[i][1])
-  }
-
-  return text
-}
+import htmlTextHelper from 'browser/lib/htmlTextHelper'
 
 const { remote } = require('electron')
 const { app } = remote
@@ -241,6 +227,13 @@ export default class MarkdownPreview extends React.Component {
     let { value, theme, indentSize, codeBlockTheme } = this.props
 
     this.refs.root.contentWindow.document.body.setAttribute('data-theme', theme)
+
+    const codeBlocks = value.match(/(```)(.|[\n])*?(```)/g)
+    if (codeBlocks !== null) {
+      codeBlocks.forEach((codeBlock) => {
+        value = value.replace(codeBlock, htmlTextHelper.encodeEntities(codeBlock))
+      })
+    }
     this.refs.root.contentWindow.document.body.innerHTML = markdown.render(value)
 
     _.forEach(this.refs.root.contentWindow.document.querySelectorAll('.taskListItem'), (el) => {
@@ -263,7 +256,7 @@ export default class MarkdownPreview extends React.Component {
       let syntax = CodeMirror.findModeByName(el.className)
       if (syntax == null) syntax = CodeMirror.findModeByName('Plain Text')
       CodeMirror.requireMode(syntax.mode, () => {
-        let content = decodeHTMLEntities(el.innerHTML)
+        let content = htmlTextHelper.decodeEntities(el.innerHTML)
         el.innerHTML = ''
         el.parentNode.className += ` cm-s-${codeBlockTheme} CodeMirror`
         CodeMirror.runMode(content, syntax.mime, el, {
@@ -281,7 +274,7 @@ export default class MarkdownPreview extends React.Component {
     _.forEach(this.refs.root.contentWindow.document.querySelectorAll('.flowchart'), (el) => {
       Raphael.setWindow(this.getWindow())
       try {
-        let diagram = flowchart.parse(decodeHTMLEntities(el.innerHTML))
+        let diagram = flowchart.parse(htmlTextHelper.decodeEntities(el.innerHTML))
         el.innerHTML = ''
         diagram.drawSVG(el, opts)
         _.forEach(el.querySelectorAll('a'), (el) => {
@@ -297,7 +290,7 @@ export default class MarkdownPreview extends React.Component {
     _.forEach(this.refs.root.contentWindow.document.querySelectorAll('.sequence'), (el) => {
       Raphael.setWindow(this.getWindow())
       try {
-        let diagram = SequenceDiagram.parse(decodeHTMLEntities(el.innerHTML))
+        let diagram = SequenceDiagram.parse(htmlTextHelper.decodeEntities(el.innerHTML))
         el.innerHTML = ''
         diagram.drawSVG(el, {theme: 'simple'})
         _.forEach(el.querySelectorAll('a'), (el) => {
diff --git a/browser/lib/htmlTextHelper.js b/browser/lib/htmlTextHelper.js
new file mode 100644
index 00000000..49952fbd
--- /dev/null
+++ b/browser/lib/htmlTextHelper.js
@@ -0,0 +1,43 @@
+/**
+ * @fileoverview Text trimmer for html.
+ */
+
+/**
+ * @param {string} text
+ * @return {string}
+ */
+
+export function decodeEntities (text) {
+  var entities = [
+    ['apos', '\''],
+    ['amp', '&'],
+    ['lt', '<'],
+    ['gt', '>'],
+    ['#63', '\\?']
+  ]
+
+  for (var i = 0, max = entities.length; i < max; ++i) {
+    text = text.replace(new RegExp(`&${entities[i][0]};`, 'g'), entities[i][1])
+  }
+
+  return text
+}
+
+export function encodeEntities (text) {
+  const entities = [
+    ['\'', 'apos'],
+    ['<', 'lt'],
+    ['>', 'gt'],
+    ['\\?', '#63']
+  ]
+
+  entities.forEach((entity) => {
+    text = text.replace(new RegExp(entity[0], 'g'), `&${entity[1]};`)
+  })
+  return text
+}
+
+export default {
+  decodeEntities,
+  encodeEntities
+}
diff --git a/tests/lib/html-text-helper-test.js b/tests/lib/html-text-helper-test.js
new file mode 100644
index 00000000..a476c0dd
--- /dev/null
+++ b/tests/lib/html-text-helper-test.js
@@ -0,0 +1,52 @@
+/**
+ * @fileoverview Unit test for browser/lib/htmlTextHelper
+ */
+const test = require('ava')
+const htmlTextHelper = require('browser/lib/htmlTextHelper')
+
+// Unit test
+test('htmlTextHelper#decodeEntities should return encoded text (string)', t => {
+  // [input, expected]
+  const testCases = [
+    ['&lt;a href=', '<a href='],
+    ['var test = &apos;test&apos;', 'var test = \'test\''],
+    ['&lt;a href=&apos;https://boostnote.io&apos;&gt;Boostnote', '<a href=\'https://boostnote.io\'>Boostnote'],
+    ['&lt;\\\\?php\n var = &apos;hoge&apos;;', '<\\\\?php\n var = \'hoge\';'],
+    ['&amp;', '&']
+  ]
+
+  testCases.forEach(testCase => {
+    const [input, expected] = testCase
+    t.is(htmlTextHelper.decodeEntities(input), expected, `Test for decodeEntities() input: ${input} expected: ${expected}`)
+  })
+})
+
+test('htmlTextHelper#decodeEntities() should return decoded text (string)', t => {
+  // [input, expected]
+  const testCases = [
+    ['<a href=', '&lt;a href='],
+    ['var test = \'test\'', 'var test = &apos;test&apos;'],
+    ['<a href=\'https://boostnote.io\'>Boostnote', '&lt;a href=&apos;https://boostnote.io&apos;&gt;Boostnote'],
+    ['<?php\n var = \'hoge\';', '&lt;&#63;php\n var = &apos;hoge&apos;;']
+  ]
+
+  testCases.forEach(testCase => {
+    const [input, expected] = testCase
+    t.is(htmlTextHelper.encodeEntities(input), expected, `Test for encodeEntities() input: ${input} expected: ${expected}`)
+  })
+})
+
+// Integration test
+test(t => {
+  const testCases = [
+    'var test = \'test\'',
+    '<a href=\'https://boostnote.io\'>Boostnote',
+    '<Component styleName=\'test\' />'
+  ]
+
+  testCases.forEach(testCase => {
+    const encodedText = htmlTextHelper.encodeEntities(testCase)
+    const decodedText = htmlTextHelper.decodeEntities(encodedText)
+    t.is(decodedText, testCase, 'Integration test through encodedText() and decodedText()')
+  })
+})