diff --git a/src/main/scala/app/SignInController.scala b/src/main/scala/app/SignInController.scala
index d7e8248..06f11cc 100644
--- a/src/main/scala/app/SignInController.scala
+++ b/src/main/scala/app/SignInController.scala
@@ -3,6 +3,8 @@
 import service._
 import util.StringUtil._
 import jp.sf.amateras.scalatra.forms._
+import util.LDAPUtil
+import service.SystemSettingsService.SystemSettings
 
 class SignInController extends SignInControllerBase with SystemSettingsService with AccountService
 
@@ -24,19 +26,11 @@
   }
 
   post("/signin", form){ form =>
-    getAccountByUserName(form.userName).collect {
-      case account if(!account.isGroupAccount && account.password == sha1(form.password)) => {
-        session.setAttribute("LOGIN_ACCOUNT", account)
-        updateLastLoginDate(account.userName)
-
-        session.get("REDIRECT").map { redirectUrl =>
-          session.removeAttribute("REDIRECT")
-          redirect(redirectUrl.asInstanceOf[String])
-        }.getOrElse {
-          redirect("/")
-        }
-      }
-    } getOrElse redirect("/signin")
+    val settings = loadSystemSettings()
+    settings.authType match {
+      case "LDAP" => ldapAuthentication(form, settings)
+      case _      => defaultAuthentication(form)
+    }
   }
 
   get("/signout"){
@@ -44,4 +38,45 @@
     redirect("/")
   }
 
+  /**
+   * Authenticate by internal database.
+   */
+  private def defaultAuthentication(form: SignInForm) = {
+    getAccountByUserName(form.userName).collect {
+      case account if(!account.isGroupAccount && account.password == sha1(form.password)) => signin(account)
+    } getOrElse redirect("/signin")
+  }
+
+  /**
+   * Authenticate by LDAP.
+   */
+  private def ldapAuthentication(form: SignInForm, settings: SystemSettings) = {
+    LDAPUtil.authenticate(settings.ldap.get, form.userName, form.password) match {
+      case Right(mailAddress) => {
+        // Create or update account by LDAP information
+        getAccountByUserName(form.userName) match {
+          case Some(x) => updateAccount(x.copy(mailAddress = mailAddress))
+          case None    => createAccount(form.userName, "", mailAddress, false, None)
+        }
+        signin(getAccountByUserName(form.userName).get)
+      }
+      case Left(errorMessage) => defaultAuthentication(form)
+    }
+  }
+
+  /**
+   * Set account information into HttpSession and redirect.
+   */
+  private def signin(account: model.Account) = {
+    session.setAttribute("LOGIN_ACCOUNT", account)
+    updateLastLoginDate(account.userName)
+
+    session.get("REDIRECT").map { redirectUrl =>
+      session.removeAttribute("REDIRECT")
+      redirect(redirectUrl.asInstanceOf[String])
+    }.getOrElse {
+      redirect("/")
+    }
+  }
+
 }
\ No newline at end of file