diff --git a/installer/renderer.js b/installer/renderer.js
index aa243e9..dc2f786 100644
--- a/installer/renderer.js
+++ b/installer/renderer.js
@@ -211,15 +211,44 @@ function renderSubStep31(host, back, done) {
 function renderSubStep32(host, back, done) {
   host.innerHTML =
     '<h3>3-2. JDK 확인</h3>' +
-    '<p class="formMessage">JAVA_HOME 또는 C:\\Program Files\\Java 에서 자동 탐색합니다. 직접 폴더를 선택해도 됩니다.</p>' +
+    '<p class="formMessage">JAVA_HOME 또는 C:\\Program Files\\Java 에서 자동 탐색합니다. 없으면 "자동 설치" 로 Temurin 21 을 받아 설치할 수 있습니다.</p>' +
     '<div class="fieldset"><label><input id="jdkPath" type="text" placeholder="C:\\Program Files\\Java\\jdk-17" value="' + (state.serverInstall.jdk || '') + '" /></label>' +
     '<button class="secondaryBtn" id="pickJdk">폴더 선택</button>' +
-    '<button class="secondaryBtn" id="auto">자동 탐색</button></div>' +
+    '<button class="secondaryBtn" id="auto">자동 탐색</button>' +
+    '<button class="secondaryBtn" id="install">자동 설치</button></div>' +
     '<div class="formMessage" id="msg"></div>' +
     '<div class="actionRow"><button class="secondaryBtn" id="back">이전</button><button class="primaryBtn" id="next">다음</button></div>'
   var input = host.querySelector('#jdkPath')
   var msg = host.querySelector('#msg')
-  host.querySelector('#auto').addEventListener('click', async function () {
+  var installBtn = host.querySelector('#install')
+  var autoBtn = host.querySelector('#auto')
+  var pickBtn = host.querySelector('#pickJdk')
+  var nextBtn = host.querySelector('#next')
+  var installing = false
+
+  function setInstallingUi(on) {
+    installing = on
+    if (on) {
+      installBtn.textContent = '설치 취소'
+      installBtn.classList.remove('secondaryBtn')
+      installBtn.classList.add('dangerBtn')
+      autoBtn.disabled = true
+      pickBtn.disabled = true
+      nextBtn.disabled = true
+      input.disabled = true
+    } else {
+      installBtn.textContent = '자동 설치'
+      installBtn.classList.remove('dangerBtn')
+      installBtn.classList.add('secondaryBtn')
+      autoBtn.disabled = false
+      pickBtn.disabled = false
+      nextBtn.disabled = false
+      input.disabled = false
+    }
+  }
+
+  autoBtn.addEventListener('click', async function () {
+    if (installing) return
     var detect = await installerApi.detectJdk()
     if (detect.found) {
       input.value = detect.path
@@ -227,16 +256,51 @@ function renderSubStep32(host, back, done) {
       msg.classList.remove('error')
       msg.classList.add('success')
     } else {
-      msg.textContent = 'JDK를 자동으로 찾지 못했습니다. 직접 선택해 주세요.'
+      msg.textContent = 'JDK를 자동으로 찾지 못했습니다. "자동 설치" 를 눌러 Temurin 21 을 설치하거나 직접 선택해 주세요.'
+      msg.classList.remove('success')
       msg.classList.add('error')
     }
   })
-  host.querySelector('#pickJdk').addEventListener('click', async function () {
+  pickBtn.addEventListener('click', async function () {
+    if (installing) return
     var picked = await installerApi.pickFolder()
     if (picked) input.value = picked
   })
-  host.querySelector('#back').addEventListener('click', back)
-  host.querySelector('#next').addEventListener('click', function () {
+  installBtn.addEventListener('click', async function () {
+    if (installing) {
+      // 진행 중이면 취소.
+      msg.textContent = 'JDK 설치 취소 요청 중...'
+      msg.classList.remove('success', 'error')
+      await installerApi.cancelJdkInstall()
+      return
+    }
+    setInstallingUi(true)
+    msg.classList.remove('success', 'error')
+    msg.textContent = 'Temurin 21 다운로드 중... (네트워크 상태에 따라 1~5분)'
+    try {
+      var result = await installerApi.installJdk()
+      if (result.ok && result.path) {
+        input.value = result.path
+        state.serverInstall.jdk = result.path
+        msg.textContent = 'JDK 자동 설치 완료: ' + result.path
+        msg.classList.add('success')
+      } else {
+        msg.textContent = 'JDK 설치 ' + (result.message === '취소됨' ? '취소됨' : '실패: ' + (result.message || '알 수 없는 오류'))
+        msg.classList.add('error')
+      }
+    } catch (err) {
+      msg.textContent = 'JDK 설치 오류: ' + (err && err.message ? err.message : err)
+      msg.classList.add('error')
+    } finally {
+      setInstallingUi(false)
+    }
+  })
+  host.querySelector('#back').addEventListener('click', function () {
+    if (installing) return
+    back()
+  })
+  nextBtn.addEventListener('click', function () {
+    if (installing) return
     if (!input.value.trim()) {
       msg.textContent = 'JDK 경로를 입력해 주세요.'
       msg.classList.add('error')
@@ -251,6 +315,8 @@ function renderSubStep32(host, back, done) {
       input.value = detect.path
       msg.textContent = 'JDK 자동 탐색됨: ' + detect.path
       msg.classList.add('success')
+    } else if (!detect.found) {
+      msg.textContent = 'JDK를 자동으로 찾지 못했습니다. "자동 설치" 를 누르면 Temurin 21 LTS 를 받아 설치합니다.'
     }
   })()
 }
diff --git a/src/installer/main.ts b/src/installer/main.ts
index a603695..72877a3 100644
--- a/src/installer/main.ts
+++ b/src/installer/main.ts
@@ -174,6 +174,8 @@ ipcMain.handle('jdk:detect', async () => {
   const candidates: string[] = []
   if (process.env.JAVA_HOME) candidates.push(process.env.JAVA_HOME)
   if (process.env.JDK_HOME) candidates.push(process.env.JDK_HOME)
+  // 자동 설치 위치(우리 설치기가 만든 JDK)도 후보에 포함.
+  candidates.push(path.join(getAppDataDir(), 'jdk', 'temurin-21'))
   candidates.push('C:\\Program Files\\Java')
 
   for (const candidate of candidates) {
@@ -204,6 +206,150 @@ ipcMain.handle('jdk:detect', async () => {
   return { found: false, path: '' }
 })
 
+// ── JDK 자동 설치(Temurin 21, 취소 가능) ──────────────────────────────
+interface JdkInstallState {
+  controller: AbortController | null
+  destDir: string | null
+  inProgress: boolean
+}
+const jdkInstall: JdkInstallState = { controller: null, destDir: null, inProgress: false }
+
+function downloadStream(
+  url: string,
+  target: string,
+  signal: AbortSignal,
+  onProgress?: (loaded: number, total: number) => void
+): Promise<void> {
+  return new Promise((resolve, reject) => {
+    if (signal.aborted) {
+      reject(new Error('취소되었습니다.'))
+      return
+    }
+    const u = new URL(url)
+    const transport = u.protocol === 'https:' ? https : http
+    const fileStream = fs.createWriteStream(target)
+    let settled = false
+    const onAbort = () => {
+      try { req.destroy(new Error('취소되었습니다.')) } catch { /* noop */ }
+      try { fileStream.close() } catch { /* noop */ }
+    }
+    signal.addEventListener('abort', onAbort)
+    const req = transport.get(u, { timeout: 120000 }, (res) => {
+      const sc = res.statusCode ?? 0
+      if (sc === 301 || sc === 302 || sc === 307 || sc === 308) {
+        const redirect = res.headers.location
+        if (redirect) {
+          res.resume()
+          fileStream.close(() => {
+            signal.removeEventListener('abort', onAbort)
+            downloadStream(new URL(redirect, u).toString(), target, signal, onProgress).then(resolve, reject)
+          })
+          return
+        }
+      }
+      if (sc >= 400) {
+        res.resume()
+        fileStream.close(() => {
+          signal.removeEventListener('abort', onAbort)
+          if (!settled) { settled = true; reject(new Error(`HTTP ${sc}`)) }
+        })
+        return
+      }
+      const total = Number(res.headers['content-length'] ?? 0)
+      let loaded = 0
+      res.on('data', (chunk: Buffer) => {
+        loaded += chunk.length
+        if (onProgress) onProgress(loaded, total)
+      })
+      res.pipe(fileStream)
+      fileStream.on('finish', () => fileStream.close(() => {
+        signal.removeEventListener('abort', onAbort)
+        if (!settled) { settled = true; resolve() }
+      }))
+      res.on('error', (err) => {
+        signal.removeEventListener('abort', onAbort)
+        if (!settled) { settled = true; reject(err) }
+      })
+    })
+    req.on('error', (err) => {
+      signal.removeEventListener('abort', onAbort)
+      fileStream.close(() => {})
+      if (!settled) { settled = true; reject(err) }
+    })
+    req.on('timeout', () => req.destroy(new Error('요청 시간 초과')))
+  })
+}
+
+ipcMain.handle('jdk:install', async (): Promise<{ ok: boolean; path?: string; message?: string }> => {
+  if (jdkInstall.inProgress) {
+    return { ok: false, message: '이미 JDK 설치가 진행 중입니다.' }
+  }
+  jdkInstall.inProgress = true
+  const controller = new AbortController()
+  jdkInstall.controller = controller
+  const tmpRoot = path.join(getAppDataDir(), 'jdk-cache')
+  await fsp.mkdir(tmpRoot, { recursive: true })
+  const tempZip = path.join(tmpRoot, `temurin-21-${Date.now()}.zip`)
+  const destDir = path.join(getAppDataDir(), 'jdk', 'temurin-21')
+  jdkInstall.destDir = destDir
+  try {
+    // Adoptium API v3: latest GA JDK 21 Windows x64. 본문은 307 로 GitHub 릴리즈로 리다이렉트.
+    const url = 'https://api.adoptium.net/v3/binary/latest/21/ga/windows/x64/jdk/hotspot/normal/eclipse?project=jdk'
+    sendLog('JDK(Temurin 21) 자동 설치 시작 — 다운로드 중...')
+    let lastPctReported = -1
+    await downloadStream(url, tempZip, controller.signal, (loaded, total) => {
+      if (total > 0) {
+        const pct = Math.floor((loaded / total) * 100)
+        if (pct >= lastPctReported + 5) {
+          lastPctReported = pct
+          sendLog(`JDK 다운로드: ${pct}% (${Math.floor(loaded / 1024 / 1024)}MB / ${Math.floor(total / 1024 / 1024)}MB)`)
+        }
+      }
+    })
+    if (controller.signal.aborted) throw new Error('취소되었습니다.')
+
+    sendLog('JDK 압축 해제 중...')
+    await fsp.rm(destDir, { recursive: true, force: true })
+    await fsp.mkdir(destDir, { recursive: true })
+    await extractZip(tempZip, { dir: destDir })
+
+    // Adoptium ZIP 은 jdk-21.x.x+... 하위 폴더로 감싸져 있다. 그 폴더의 bin/java.exe 가 실제 자바.
+    let javaRoot = destDir
+    const inner = await fsp.readdir(destDir, { withFileTypes: true })
+    const innerJdk = inner.find((entry) => entry.isDirectory() && /^jdk-/i.test(entry.name))
+    if (innerJdk) javaRoot = path.join(destDir, innerJdk.name)
+    const javaExe = path.join(javaRoot, 'bin', process.platform === 'win32' ? 'java.exe' : 'java')
+    if (!fs.existsSync(javaExe)) {
+      throw new Error(`설치 후 java 실행 파일을 찾지 못했습니다: ${javaExe}`)
+    }
+
+    sendLog(`JDK 자동 설치 완료: ${javaRoot}`)
+    return { ok: true, path: javaRoot }
+  } catch (err) {
+    const msg = (err as Error).message || String(err)
+    if (controller.signal.aborted || /취소/.test(msg)) {
+      sendLog('JDK 설치가 취소되었습니다.')
+      try { await fsp.rm(destDir, { recursive: true, force: true }) } catch { /* noop */ }
+      return { ok: false, message: '취소됨' }
+    }
+    sendLog(`JDK 설치 실패: ${msg}`)
+    return { ok: false, message: msg }
+  } finally {
+    try { await fsp.rm(tempZip, { force: true }) } catch { /* noop */ }
+    jdkInstall.inProgress = false
+    jdkInstall.controller = null
+    jdkInstall.destDir = null
+  }
+})
+
+ipcMain.handle('jdk:cancelInstall', async (): Promise<{ ok: boolean }> => {
+  if (jdkInstall.controller) {
+    jdkInstall.controller.abort()
+    sendLog('JDK 설치 취소 요청을 보냈습니다.')
+  }
+  return { ok: true }
+})
+
 /**
  * 입력값이 절대 URL이면 그대로, 상대값이면 manifest 도메인의 /file/<subDir>/<file> 로 해석.
  */
diff --git a/src/installer/preload.ts b/src/installer/preload.ts
index acdc9a6..c77b503 100644
--- a/src/installer/preload.ts
+++ b/src/installer/preload.ts
@@ -15,6 +15,8 @@ const api = {
 
   // 3-2
   detectJdk: (): Promise<{ found: boolean; path: string }> => ipcRenderer.invoke('jdk:detect'),
+  installJdk: (): Promise<{ ok: boolean; path?: string; message?: string }> => ipcRenderer.invoke('jdk:install'),
+  cancelJdkInstall: (): Promise<{ ok: boolean }> => ipcRenderer.invoke('jdk:cancelInstall'),
 
   // 3-3
   startServerInstall: (payload: ServerInstallPayload): Promise<void> =>