diff --git a/packages/example/articles/example.md b/packages/example/articles/example.md
index de9b4bc1..7722231d 100644
--- a/packages/example/articles/example.md
+++ b/packages/example/articles/example.md
@@ -135,4 +135,193 @@ $a^*b$ with $a^*$
 $\sum_{i=1}^n$	
 fafa
 
-a
\ No newline at end of file
+a
+
+
+
+## mermaid.js
+
+```mermaid
+%%{init: { 'theme': 'forest' } }%%
+graph LR;
+    A-->B & C-->D & E-->F & Z-->X;
+    F-->G
+    G-->H
+    H-->I
+    I-->J
+    J-->K
+    K-->L
+    L-->M
+    M-->N
+    N-->O
+    O-->P
+    P-->ID1[ノード1<br>ノード2]
+```
+
+### flowchart
+
+```mermaid
+flowchart TB
+    c1-->a2
+    subgraph one
+    a1-->a2
+    end
+    subgraph two
+    b1-->b2
+    end
+    subgraph three
+    c1-->c2
+    end
+    one --> two
+    three --> two
+    two --> c2
+```
+
+### sequence diagram
+
+```mermaid
+sequenceDiagram
+    autonumber
+    アリス->>光輝: Hello John, how are you?
+    loop Healthcheck
+        光輝->>光輝: Fight against hypochondria
+    end
+    Note right of 光輝: Rational thoughts!
+    光輝-->>アリス: Great!
+    光輝->>Bob: How about you?
+    Bob-->>光輝: Jolly good!
+```
+
+### class diagram
+
+```mermaid
+ classDiagram
+      Animal <|-- Duck
+      Animal <|-- Fish
+      Animal <|-- Zebra
+      Animal : +int age
+      Animal : +String gender
+      Animal: +isMammal()
+      Animal: +mate()
+      class Duck{
+          +String beakColor
+          +swim()
+          +quack()
+      }
+      class Fish{
+          -int sizeInFeet
+          -canEat()
+      }
+      class Zebra{
+          +bool is_wild
+          +run()
+      }
+```
+
+
+### state diagram
+
+```mermaid
+stateDiagram-v2
+    [*] --> Active
+
+    state Active {
+        [*] --> NumLockOff
+        NumLockOff --> NumLockOn : EvNumLockPressed
+        NumLockOn --> NumLockOff : EvNumLockPressed
+        --
+        [*] --> CapsLockOff
+        CapsLockOff --> CapsLockOn : EvCapsLockPressed
+        CapsLockOn --> CapsLockOff : EvCapsLockPressed
+        --
+        [*] --> ScrollLockOff
+        ScrollLockOff --> ScrollLockOn : EvScrollLockPressed
+        ScrollLockOn --> ScrollLockOff : EvScrollLockPressed
+        
+    }
+```
+
+
+
+```mermaid
+graph LR
+A:::someclass  B
+classDef someclass fill:#f96;
+classDef someclass fill:#f96;
+classDef someclass fill:#f96;
+classDef someclass fill:#f96;
+classDef someclass fill:#f96;
+classDef someclass fill:#f96;
+classDef someclass fill:#f96;
+classDef someclass fill:#f96;
+classDef someclass fill:#f96;
+classDef someclass fill:#f96;
+classDef someclass fill:#f96;
+classDef someclass fill:#f96;
+classDef someclass fill:#f96;
+classDef someclass fill:#f96;
+classDef someclass fill:#f96;
+classDef someclass fill:#f96;
+classDef someclass fill:#f96;
+classDef someclass fill:#f96;
+classDef someclass fill:#f96;
+classDef someclass fill:#f96;
+classDef someclass fill:#f96;
+classDef someclass fill:#f96;
+classDef someclass fill:#f96;
+classDef someclass fill:#f96;
+classDef someclass fill:#f96;
+classDef someclass fill:#f96;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+    A-->B & C-->D & E-->F & Z-->X;
+```
+
+
+```mermaid
+graph LR;
+    A["<img src=invalid onerror=alert('XSS')></img>"] --> B;
+    alert`md5_salt`-->B;
+    click alert`md5_salt` eval "Tooltip for a callback"
+    click B "javascript:alert('XSS')" "This is a tooltip for a link"
+```
+
+```mermaid
+graph LR;
+    alert`md5_salt`-->B;
+    click alert`md5_salt` eval "Tooltip for a callback"
+    click B "javascript:alert('XSS')" "This is a tooltip for a link"
+    link Zebra "http://www.github.com" "This is a link"
+```
diff --git a/packages/zenn-embed-elements/src/classes/mermaid.ts b/packages/zenn-embed-elements/src/classes/mermaid.ts
new file mode 100644
index 00000000..3703252b
--- /dev/null
+++ b/packages/zenn-embed-elements/src/classes/mermaid.ts
@@ -0,0 +1,164 @@
+/**
+ * original: https://github.com/gitlabhq/gitlabhq/blob/master/app/assets/javascripts/behaviors/markdown/render_mermaid.js
+ */
+
+import { loadScript } from '../utils/load-script';
+
+// レンダリングする図ごとの最大文字数
+const MAX_CHAR_LIMIT = 2000;
+
+// https://mermaid-js.github.io/mermaid/#/flowchart?id=chaining-of-links
+// 新しい仕様で
+// graph LR
+//    a --> b & c--> d
+// に対応するが、少ない記述でノード接続が爆発する可能性があるため最大数を制限する
+const MAX_CHAINING_OF_LINKS_LIMIT = 10;
+
+// Page values
+declare let mermaid: any;
+const containerId = 'mermaid-container';
+
+async function initMermaid(): Promise<void> {
+  if (typeof mermaid === 'undefined') {
+    await loadScript({
+      src: 'https://cdn.jsdelivr.net/npm/mermaid@8.10/dist/mermaid.min.js',
+      id: 'mermaid-js',
+    });
+    const theme = 'default';
+
+    // mermaid 本体がロード時に走らないように設定
+    // mermaid 本体は使わないのでほかは設定しない
+    mermaid!.initialize({
+      mermaid: {
+        startOnLoad: false,
+      },
+    });
+
+    // mermaidAPI の設定
+    mermaid!.mermaidAPI.initialize({
+      startOnLoad: false, // レンダリングはこちらでやるので false
+      securityLevel: 'strict', // tags in text are encoded, click functionality is disabled
+      theme,
+      er: {
+        useMaxWidth: true,
+      },
+      flowchart: {
+        useMaxWidth: true, // 表示の都合上見切れるのもスクロールするのも嫌なので最大幅を有効にする
+        htmlLabels: false, // セキュリティのため、HTMLラベルは許可しない
+      },
+      sequence: {
+        useMaxWidth: true,
+      },
+    });
+  }
+}
+
+type ErrorContainer = {
+  yes: boolean;
+  message: string;
+};
+
+type PotentialRisk = {
+  syntaxError: ErrorContainer;
+  charLimitOver: ErrorContainer;
+  chainingOfLinksOver: ErrorContainer;
+};
+
+function getPotentialPerformanceRisk(source: string): PotentialRisk {
+  const cool = (() => {
+    try {
+      mermaid!.mermaidAPI.parse(source);
+      return true;
+    } catch (e) {
+      console.log(
+        'mermaid.js のレンダリングでシンタックスエラーが発生しました',
+        e
+      );
+      return false;
+    }
+  })();
+  return {
+    syntaxError: {
+      yes: !cool,
+      message: `<li>シンタックスエラーです</li>`,
+    },
+    charLimitOver: {
+      yes: source.length > MAX_CHAR_LIMIT,
+      message: `<li>ブロックあたりの文字数上限は${MAX_CHAR_LIMIT}です</li>`,
+    },
+    chainingOfLinksOver: {
+      yes: (source.match(/&/g) || []).length > MAX_CHAINING_OF_LINKS_LIMIT,
+      message: `<li>ブロックあたりの&によるチェイン上限は${MAX_CHAINING_OF_LINKS_LIMIT}です</li>`,
+    },
+  };
+}
+
+export class EmbedMermaid extends HTMLElement {
+  // mermaid のソース記述が格納されているpreタグ
+  private readonly _sourceContainer: HTMLPreElement;
+
+  // 描画後の svg を格納するdivタグ ここで作る
+  private readonly _svgContainer: HTMLDivElement;
+
+  constructor() {
+    super();
+
+    // コード記述が格納されている pre タグを取得
+    this._sourceContainer = this.childNodes[0] as HTMLPreElement;
+
+    // 描画後のSVGを格納する div タグを作成
+    const container = document.createElement('div');
+    this.appendChild(container);
+    this._svgContainer = container;
+  }
+
+  async connectedCallback() {
+    this.render();
+  }
+
+  async render() {
+    await initMermaid();
+    const source = this._sourceContainer.innerText || '';
+
+    // Mermaid モジュールの読み込みに失敗したり、レンダリング対象のコンテンツが空の場合は何もせずに終了
+    if (!source) {
+      return;
+    }
+
+    // 文法エラーやパフォーマンスリスクが検出された場合、注意書きをレンダリングして終了
+    const risk = getPotentialPerformanceRisk(source);
+    if (
+      Object.values(risk)
+        .map((r) => r.yes)
+        .includes(true)
+    ) {
+      this.innerHTML = `
+       <p>
+        <span>mermaidをレンダリングできません。</span>
+        <ul>
+        ${risk.syntaxError.yes ? risk.syntaxError.message : ''}
+        ${risk.charLimitOver.yes ? risk.charLimitOver.message : ''}
+        ${risk.chainingOfLinksOver.yes ? risk.chainingOfLinksOver.message : ''}
+        </ul>
+       </p>
+      `;
+      return;
+    }
+
+    // すべて通過した場合はレンダリングする
+    // セキュリティリスクを考慮して bindFunctions は実行しない方針にする
+    // 今回は `securityLevel='strict'` にしているのでどのみち実行されない
+    // securityLevel='loose'にし、かつ `Interaction` を有効にする場合は
+    // https://github.com/mermaidjs/mermaid-gitbook/blob/master/content/usage.md#binding-events
+    // ここを参考に追加する
+    const insert = (svgCode: string, bindFunctions: any) => {
+      this._svgContainer.innerHTML = svgCode;
+    };
+    mermaid?.mermaidAPI.render(
+      `${containerId}-${Date.now().valueOf()}-render`,
+      source,
+      insert,
+      this._sourceContainer
+    );
+  }
+}
diff --git a/packages/zenn-embed-elements/src/index.ts b/packages/zenn-embed-elements/src/index.ts
index 12373376..8de07abe 100644
--- a/packages/zenn-embed-elements/src/index.ts
+++ b/packages/zenn-embed-elements/src/index.ts
@@ -1,7 +1,9 @@
 import { EmbedGist } from './classes/gist';
 import { EmbedTweet } from './classes/tweet';
 import { EmbedKatex } from './classes/katex';
+import { EmbedMermaid } from './classes/mermaid';
 
 customElements.define('embed-gist', EmbedGist);
 customElements.define('embed-tweet', EmbedTweet);
 customElements.define('embed-katex', EmbedKatex);
+customElements.define('embed-mermaid', EmbedMermaid);
diff --git a/packages/zenn-markdown-html/__tests__/mermaid.test.ts b/packages/zenn-markdown-html/__tests__/mermaid.test.ts
new file mode 100644
index 00000000..f9af4f02
--- /dev/null
+++ b/packages/zenn-markdown-html/__tests__/mermaid.test.ts
@@ -0,0 +1,24 @@
+import markdownToHtml from '../src/index';
+
+describe('Detect mermaid property', () => {
+  test('should generate TD valid code format html', () => {
+    const html = markdownToHtml(`\`\`\`mermaid\ngraph TD\nA --> B\n\`\`\``);
+    expect(html).toContain(
+      '<div class="embed-mermaid"><embed-mermaid><pre class="zenn-mermaid">graph TD\nA --&gt; B</pre></embed-mermaid></div>'
+    );
+  });
+  test('should keep directive', () => {
+    const html = markdownToHtml(`\`\`\`mermaid\n%%{init: { 'theme': 'forest' } }%%\ngraph TD\nA --> B\n\`\`\``);
+    expect(html).toContain(
+      '<div class="embed-mermaid"><embed-mermaid><pre class="zenn-mermaid">%%{init: { \'theme\': \'forest\' } }%%\ngraph TD\nA --&gt; B</pre></embed-mermaid></div>'
+    );
+  });
+  test('should escape html tag', () => {
+    const html = markdownToHtml(
+      `\`\`\`mermaid\ngraph TD\nA --> B\n<br><script>alert("XSS")</script>\`\`\``
+    );
+    expect(html).toContain(
+      '<div class="embed-mermaid"><embed-mermaid><pre class="zenn-mermaid">graph TD\nA --&gt; B\n&lt;br&gt;&lt;script&gt;alert(&quot;XSS&quot;)&lt;/script&gt;```</pre></embed-mermaid></div>'
+    );
+  });
+});
diff --git a/packages/zenn-markdown-html/__tests__/xss.test.ts b/packages/zenn-markdown-html/__tests__/xss.test.ts
index 5178d02b..286d2cbf 100644
--- a/packages/zenn-markdown-html/__tests__/xss.test.ts
+++ b/packages/zenn-markdown-html/__tests__/xss.test.ts
@@ -44,4 +44,12 @@ describe('No XSS Vulnerability', () => {
       '<pre class="language-&quot;&gt;&lt;img/onerror=&quot;alert(location)&quot;src=.&gt;"><code class="language-&quot;&gt;&lt;img/onerror=&quot;alert(location)&quot;src=.&gt;">'
     );
   });
+  test('should escape img tag around mermaid syntax', () => {
+    const html = markdownToHtml(
+      `\`\`\`mermaid\ngraph TD\nA["<img src="invalid" onerror=alert('XSS')/>"] --> B\`\`\``
+    );
+    expect(html).toContain(
+      '<div class="embed-mermaid"><embed-mermaid><pre class="zenn-mermaid">graph TD\nA[&quot;&lt;img src=&quot;invalid&quot; onerror=alert(\'XSS\')/&gt;&quot;] --&gt; B```</pre></embed-mermaid></div>'
+    );
+  });
 });
diff --git a/packages/zenn-markdown-html/jest.config.js b/packages/zenn-markdown-html/jest.config.js
index 4805cba6..c42bb78c 100644
--- a/packages/zenn-markdown-html/jest.config.js
+++ b/packages/zenn-markdown-html/jest.config.js
@@ -2,7 +2,7 @@ module.exports = {
   globals: {
     'ts-jest': {
       // avoid "jsx" treated as "preserved"
-      tsConfig: 'tsconfig.json',
+      tsconfig: 'tsconfig.json',
     },
   },
   moduleFileExtensions: ['js', 'json', 'ts'],
diff --git a/packages/zenn-markdown-html/src/index.ts b/packages/zenn-markdown-html/src/index.ts
index 4c91eb16..ffd1ac13 100644
--- a/packages/zenn-markdown-html/src/index.ts
+++ b/packages/zenn-markdown-html/src/index.ts
@@ -14,6 +14,7 @@ import { mdBr } from './utils/md-br';
 import { mdCustomBlock } from './utils/md-custom-block';
 import markdownItImSize from '@steelydylan/markdown-it-imsize';
 import markdownItAnchor from 'markdown-it-anchor';
+import { mdMermaid } from './utils/md-mermaid';
 
 const mdContainer = require('markdown-it-container');
 const mdFootnote = require('markdown-it-footnote');
@@ -52,7 +53,8 @@ md.use(mdBr)
     },
   })
   .use(mdKatex)
-  .use(mdLinkifyToCard);
+  .use(mdLinkifyToCard)
+  .use(mdMermaid);
 
 // custom footnote => TODO: ファイルを分ける
 md.renderer.rules.footnote_block_open = () =>
diff --git a/packages/zenn-markdown-html/src/utils/md-mermaid.ts b/packages/zenn-markdown-html/src/utils/md-mermaid.ts
new file mode 100644
index 00000000..242d0d0e
--- /dev/null
+++ b/packages/zenn-markdown-html/src/utils/md-mermaid.ts
@@ -0,0 +1,19 @@
+import MarkdownIt from 'markdown-it';
+
+export function mdMermaid(md: MarkdownIt) {
+  const defaultRender =
+    md.renderer.rules.fence ||
+    function (tokens, idx, options, env, self) {
+      return self.renderToken(tokens, idx, options);
+    };
+  md.renderer.rules.fence = (tokens, idx, options, env, slf) => {
+    const langInfo = tokens[idx];
+    if (langInfo.info === 'mermaid') {
+      const code = langInfo.content.trim();
+      return `<div class="embed-mermaid"><embed-mermaid><pre class="zenn-mermaid">${md.utils.escapeHtml(
+        code
+      )}</pre></embed-mermaid></div>`;
+    }
+    return defaultRender(tokens, idx, options, env, slf);
+  };
+}