diff --git a/lib/fluent/command/fluentd.rb b/lib/fluent/command/fluentd.rb
index b2b737c1f2..d14d8fece6 100644
--- a/lib/fluent/command/fluentd.rb
+++ b/lib/fluent/command/fluentd.rb
@@ -335,5 +335,18 @@
   end
   worker = Fluent::Supervisor.new(opts)
   worker.configure
-  worker.run_worker
+
+  if opts[:daemonize]
+    require 'fluent/daemonizer'
+    args = ARGV.dup
+    i = args.index('--daemon')
+    args.delete_at(i + 1)          # value of --daemon
+    args.delete_at(i)              # --daemon itself
+
+    Fluent::Daemonizer.daemonize(opts[:daemonize], args) do
+      worker.run_worker
+    end
+  else
+    worker.run_worker
+  end
 end
diff --git a/lib/fluent/daemonizer.rb b/lib/fluent/daemonizer.rb
new file mode 100644
index 0000000000..3549d13fbf
--- /dev/null
+++ b/lib/fluent/daemonizer.rb
@@ -0,0 +1,88 @@
+#
+# Fluentd
+#
+#    Licensed under the Apache License, Version 2.0 (the "License");
+#    you may not use this file except in compliance with the License.
+#    You may obtain a copy of the License at
+#
+#        http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS,
+#    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#    See the License for the specific language governing permissions and
+#    limitations under the License.
+#
+
+require 'fluent/config/error'
+
+module Fluent
+  class Daemonizer
+    def self.daemonize(pid_path, args = [], &block)
+      new.daemonize(pid_path, args, &block)
+    end
+
+    def daemonize(pid_path, args = [])
+      pid_fullpath = File.absolute_path(pid_path)
+      check_pidfile(pid_fullpath)
+
+      begin
+        Process.daemon(false, false)
+
+        File.write(pid_fullpath, Process.pid.to_s)
+
+        # install signal and set process name are performed by supervisor
+        install_at_exit_handlers(pid_fullpath)
+
+        yield
+      rescue NotImplementedError
+        daemonize_with_spawn(pid_fullpath, args)
+      end
+    end
+
+    private
+
+    def daemonize_with_spawn(pid_fullpath, args)
+      pid = Process.spawn(*['fluentd'].concat(args))
+
+      File.write(pid_fullpath, pid.to_s)
+
+      pid
+    end
+
+    def check_pidfile(pid_path)
+      if File.exist?(pid_path)
+        if !File.readable?(pid_path) || !File.writable?(pid_path)
+          raise Fluent::ConfigError, "Cannot access pid file: #{pid_path}"
+        end
+
+        pid =
+          begin
+            Integer(File.read(pid_path), 10)
+          rescue TypeError, ArgumentError
+            return # ignore
+          end
+
+        begin
+          Process.kill(0, pid)
+          raise Fluent::ConfigError, "pid(#{pid}) is running"
+        rescue Errno::EPERM
+          raise Fluent::ConfigError, "pid(#{pid}) is running"
+        rescue Errno::ESRCH
+        end
+      else
+        unless File.writable?(File.dirname(pid_path))
+          raise Fluent::ConfigError, "Cannot access directory for pid file: #{File.dirname(pid_path)}"
+        end
+      end
+    end
+
+    def install_at_exit_handlers(pidfile)
+      at_exit do
+        if File.exist?(pidfile)
+          File.delete(pidfile)
+        end
+      end
+    end
+  end
+end
diff --git a/test/test_daemonizer.rb b/test/test_daemonizer.rb
new file mode 100644
index 0000000000..c4344f1ed5
--- /dev/null
+++ b/test/test_daemonizer.rb
@@ -0,0 +1,91 @@
+require_relative 'helper'
+require 'fluent/daemonizer'
+
+class DaemonizerTest < ::Test::Unit::TestCase
+  TMP_DIR = File.join(File.dirname(__FILE__), 'tmp', 'daemonizer')
+
+  setup do
+    FileUtils.mkdir_p(TMP_DIR)
+  end
+
+  teardown do
+    FileUtils.rm_rf(TMP_DIR) rescue nil
+  end
+
+  test 'makes pid file' do
+    pid_path = File.join(TMP_DIR, 'file.pid')
+
+    mock(Process).daemon(anything, anything).once
+    r = Fluent::Daemonizer.daemonize(pid_path) { 'ret' }
+    assert_equal 'ret', r
+    assert File.exist?(pid_path)
+    assert Process.pid.to_s, File.read(pid_path).to_s
+  end
+
+  test 'in platforms which do not support fork' do
+    pid_path = File.join(TMP_DIR, 'file.pid')
+
+    mock(Process).daemon(anything, anything) { raise NotImplementedError }
+    args = ['-c', 'test.conf']
+    mock(Process).spawn(anything, *args) { Process.pid }
+
+    Fluent::Daemonizer.daemonize(pid_path, args) { 'ret' }
+    assert File.exist?(pid_path)
+    assert Process.pid.to_s, File.read(pid_path).to_s
+  end
+
+  sub_test_case 'when pid file already exists' do
+    test 'raise an error when process is running' do
+      omit 'chmod of file does not affetct root user' if Process.uid.zero?
+      pid_path = File.join(TMP_DIR, 'file.pid')
+      File.write(pid_path, '1')
+
+      mock(Process).daemon(anything, anything).never
+      mock(Process).kill(0, 1).once
+
+      assert_raise(Fluent::ConfigError.new('pid(1) is running')) do
+        Fluent::Daemonizer.daemonize(pid_path) { 'ret' }
+      end
+    end
+
+    test 'raise an error when file is not redable' do
+      omit 'chmod of file does not affetct root user' if Process.uid.zero?
+      not_readable_path = File.join(TMP_DIR, 'not_readable.pid')
+
+      File.write(not_readable_path, '1')
+      FileUtils.chmod(0333, not_readable_path)
+
+      mock(Process).daemon(anything, anything).never
+      assert_raise(Fluent::ConfigError.new("Cannot access pid file: #{File.absolute_path(not_readable_path)}")) do
+        Fluent::Daemonizer.daemonize(not_readable_path) { 'ret' }
+      end
+    end
+
+    test 'raise an error when file is not writable' do
+      omit 'chmod of file does not affetct root user' if Process.uid.zero?
+      not_writable_path = File.join(TMP_DIR, 'not_writable.pid')
+
+      File.write(not_writable_path, '1')
+      FileUtils.chmod(0555, not_writable_path)
+
+      mock(Process).daemon(anything, anything).never
+      assert_raise(Fluent::ConfigError.new("Cannot access pid file: #{File.absolute_path(not_writable_path)}")) do
+        Fluent::Daemonizer.daemonize(not_writable_path) { 'ret' }
+      end
+    end
+
+    test 'raise an error when directory is not writable' do
+      omit 'chmod of file does not affetct root user' if Process.uid.zero?
+      not_writable_dir = File.join(TMP_DIR, 'not_writable')
+      pid_path = File.join(not_writable_dir, 'file.pid')
+
+      FileUtils.mkdir_p(not_writable_dir)
+      FileUtils.chmod(0555, not_writable_dir)
+
+      mock(Process).daemon(anything, anything).never
+      assert_raise(Fluent::ConfigError.new("Cannot access directory for pid file: #{File.absolute_path(not_writable_dir)}")) do
+        Fluent::Daemonizer.daemonize(pid_path) { 'ret' }
+      end
+    end
+  end
+end