diff --git a/.travis.yml b/.travis.yml
index ebe996a..ef8a475 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,4 +1,9 @@
+dist: xenial
 language: python
+cache:
+  pip: true
+  directories:
+  - "$TRAVIS_BUILD_DIR/.tox"
 
 python:
   - 2.7
@@ -9,6 +14,10 @@ env:
   global:
     MACKEREL_APIKEY='xxxxxxxx'
 
-before_install: pip install -r requirements.txt
+before_install:
+  - pip install -U -r requirements.txt
+before_script:
+  - flake8 --verbose --jobs=8
 
-script: python setup.py test
+script:
+  - python setup.py test
diff --git a/mackerel/__init__.py b/mackerel/__init__.py
index de40ea7..68c04af 100644
--- a/mackerel/__init__.py
+++ b/mackerel/__init__.py
@@ -1 +1,2 @@
+# -*- coding: utf-8 -*-
 __import__('pkg_resources').declare_namespace(__name__)
diff --git a/mackerel/client.py b/mackerel/client.py
index da1e110..44be228 100644
--- a/mackerel/client.py
+++ b/mackerel/client.py
@@ -13,6 +13,7 @@
     :license: BSD, see LICENSE for more details.
 """
 import logging
+
 import requests
 import simplejson as json
 from mackerel.host import Host
@@ -25,7 +26,7 @@ class MackerelClientError(Exception):
 class Client(object):
 
     #: Mackerel apikey error message.
-    ERROR_MESSAGE_FOR_API_KEY_ABSENCE = 'API key is absent. Set your API key in a environment variable called MACKEREL_APIKEY.'
+    ERROR_MESSAGE_FOR_API_KEY_ABSENCE = 'API key is absent. Set your API key in a environment variable called MACKEREL_APIKEY.' # noqa E501
     #: Log format.
     debug_log_format = (
         '[%(asctime)s %(levelname)s][%(pathname)s:%(lineno)d]: %(message)s'
@@ -44,8 +45,7 @@ def __init__(self, logger=None, **kwargs):
 
         self.api_key = api_key
         if logger is None:
-            logging.basicConfig(level=logging.INFO,
-                                format=self.debug_log_format)
+            logging.basicConfig(level=logging.INFO, format=self.debug_log_format)
             self.logger = logging.getLogger('mackerel.client')
         else:
             self.logger = logger
@@ -176,8 +176,9 @@ def _request(self, uri, method='GET', headers=None, params=None):
             message = '{0} is not supported.'.format(method)
             raise NotImplementedError(message)
 
-        self.logger.debug('Response from {0} is {1}'.format(self.origin,
-                                                            res.status_code))
+        self.logger.debug(
+            'Response from {0} is {1}'.format(self.origin, res.status_code),
+        )
         if res.status_code != 200:
             message = '{0} {1} failed: {2}'.format(method, uri, res.status_code)
             raise MackerelClientError(message)
diff --git a/mackerel/host.py b/mackerel/host.py
index c6d27e1..0967376 100644
--- a/mackerel/host.py
+++ b/mackerel/host.py
@@ -57,10 +57,20 @@ def mac_addr(self):
                 return i['macAddress']
 
     def __repr__(self):
+        """Host instance."""
         repr = '<Host('
         repr += 'name={0}, meta={1}, type={2}, status={3}, memo={4},'
         repr += 'is_retired={5}, id={6}, created_at={7}, roles={8},'
         repr += 'interfaces={9})'
-        return repr.format(self.name, self.meta, self.type, self.status,
-                           self.memo, self.is_retired, self.id,
-                           self.created_at, self.roles, self.interfaces)
+        return repr.format(
+            self.name,
+            self.meta,
+            self.type,
+            self.status,
+            self.memo,
+            self.is_retired,
+            self.id,
+            self.created_at,
+            self.roles,
+            self.interfaces,
+        )
diff --git a/mackerel/runner.py b/mackerel/runner.py
index d2568f4..5e370ee 100644
--- a/mackerel/runner.py
+++ b/mackerel/runner.py
@@ -12,8 +12,9 @@
     :copyright: (c) 2015 Shinya Ohyanagi, All rights reserved.
     :license: BSD, see LICENSE for more details.
 """
-import os
 import logging
+import os
+
 import click
 from mackerel.client import Client
 
diff --git a/requirements.txt b/requirements.txt
index 0e763f5..1670199 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -2,3 +2,12 @@ requests==2.22.0
 click==7.0
 simplejson==3.16.0
 mock==3.0.5
+flake8==3.7.8
+flake8-coding==1.3.2
+flake8-commas==2.0.0
+flake8-comprehensions==1.4.1 # pyup: <2.0
+flake8-debugger==3.1.0
+flake8-docstrings==1.4.0
+flake8-import-order==0.18.1
+flake8-print==3.1.0
+flake8-string-format==0.2.3
diff --git a/setup.cfg b/setup.cfg
new file mode 100644
index 0000000..29cd264
--- /dev/null
+++ b/setup.cfg
@@ -0,0 +1,15 @@
+[flake8]
+max-line-length = 120
+exclude =
+  .cache,
+  .git,
+  .tox,
+  build,
+  migrations,
+  venv,
+  __pycache__
+ignore = D100,D101,D102,D103,D104,D106,D107,D205,D208,D400
+import-order-style = smarkets
+
+[wheel]
+universal = 1
diff --git a/setup.py b/setup.py
index 1116386..86c5a61 100644
--- a/setup.py
+++ b/setup.py
@@ -10,7 +10,11 @@
     :license: BSD, see LICENSE for more details.
 """
 import os
-from setuptools import setup, find_packages
+
+from setuptools import (
+    find_packages,
+    setup,
+)
 
 requires = ['requests', 'simplejson', 'click']
 
@@ -41,12 +45,12 @@
         'Intended Audience :: Developers',
         'License :: OSI Approved :: BSD License',
         'Operating System :: OS Independent',
-        'Programming Language :: Python'
+        'Programming Language :: Python',
     ],
     entry_points="""
     [console_scripts]
     mkr.py = mackerel.runner:main
     """,
     tests_require=['requests', 'simplejson', 'mock'],
-    test_suite='tests'
+    test_suite='tests',
 )
diff --git a/tests/test_client.py b/tests/test_client.py
index 308f8f7..5cd8e07 100644
--- a/tests/test_client.py
+++ b/tests/test_client.py
@@ -10,11 +10,15 @@
     :license: BSD, see LICENSE for more details.
 """
 import os
-import requests
 from unittest import TestCase
-from mock import patch
-from mackerel.client import Client, MackerelClientError
+
+import requests
+from mackerel.client import (
+    Client,
+    MackerelClientError,
+)
 from mackerel.host import Host
+from mock import patch
 
 
 def dummy_response(m, filename, status_code=200):
@@ -37,7 +41,7 @@ def setUpClass(cls):
 
     @patch('mackerel.client.requests.get')
     def test_should_get_hosts(self, m):
-        """ Client().get_hosts() should get host list. """
+        """Client().get_hosts() should get host list."""
         dummy_response(m, 'fixtures/get_hosts.json')
         hosts = self.client.get_hosts()
         for host in hosts:
@@ -45,14 +49,14 @@ def test_should_get_hosts(self, m):
 
     @patch('mackerel.client.requests.get')
     def test_should_get_host(self, m):
-        """ Client().get_hosts() should get host. """
+        """Client().get_hosts() should get host."""
         dummy_response(m, 'fixtures/get_host.json')
         host = self.client.get_host(self.id)
         self.assertTrue(isinstance(host, Host))
 
     @patch('mackerel.client.requests.post')
     def test_should_update_host_poweroff(self, m):
-        """ Client().update_host_status('poweroff') should return success. """
+        """Client().update_host_status('poweroff') should return success."""
         dummy_response(m, 'fixtures/success.json')
         ret = self.client.update_host_status(self.id, 'poweroff')
         self.assertEqual(ret['success'], True)
@@ -63,7 +67,7 @@ def test_should_update_host_poweroff(self, m):
 
     @patch('mackerel.client.requests.post')
     def test_should_update_host_standby(self, m):
-        """ Client().update_host_status('standby') should return success. """
+        """Client().update_host_status('standby') should return success."""
         dummy_response(m, 'fixtures/success.json')
         ret = self.client.update_host_status(self.id, 'standby')
         self.assertEqual(ret['success'], True)
@@ -75,7 +79,7 @@ def test_should_update_host_standby(self, m):
 
     @patch('mackerel.client.requests.post')
     def test_should_update_host_working(self, m):
-        """ Client().update_host_status('working') should return success. """
+        """Client().update_host_status('working') should return success."""
         dummy_response(m, 'fixtures/success.json')
         ret = self.client.update_host_status('2k48zsCx8ij', 'working')
         self.assertEqual(ret['success'], True)
@@ -86,7 +90,7 @@ def test_should_update_host_working(self, m):
 
     @patch('mackerel.client.requests.post')
     def test_should_update_host_maintenance(self, m):
-        """ Client().update_host_status('maintenance') should return success. """
+        """Client().update_host_status('maintenance') should return success."""
         dummy_response(m, 'fixtures/success.json')
         ret = self.client.update_host_status(self.id, 'maintenance')
         self.assertEqual(ret['success'], True)
@@ -96,40 +100,42 @@ def test_should_update_host_maintenance(self, m):
             self.assertEqual(host.status, 'maintenance')
 
     def test_should_update_host_invalid(self):
-        """ Client().update_host_status('foo') should raise error. """
+        """Client().update_host_status('foo') should raise error."""
         with self.assertRaises(MackerelClientError):
             self.client.update_host_status(self.id, 'foo')
 
     @patch('mackerel.client.requests.post')
     def test_should_retire(self, m):
-        """ Client().retire_host() should return success. """
+        """Client().retire_host() should return success."""
         dummy_response(m, 'fixtures/success.json')
         ret = self.client.retire_host(self.id)
         self.assertEqual(ret['success'], True)
 
     @patch('mackerel.client.requests.get')
     def test_should_get_latest_metrics(self, m):
-        """ Client().get_latest_metrics() should get metrics. """
+        """Client().get_latest_metrics() should get metrics."""
         dummy_response(m, 'fixtures/get_latest_metrics.json')
-        ret = self.client.get_latest_metrics([self.id],
-                                             ['loadavg5', 'memory.free'])
+        ret = self.client.get_latest_metrics(
+            [self.id],
+            ['loadavg5', 'memory.free'],
+        )
         for k in ['loadavg5', 'memory.free']:
             self.assertTrue(k in ret['tsdbLatest'][self.id].keys())
 
     @patch('mackerel.client.requests.post')
     def test_should_post_metrics(self, m):
-        """ Client().post_metrics() should return success. """
+        """Client().post_metrics() should return success."""
         dummy_response(m, 'fixtures/success.json')
         id = self.id
         metrics = [
             {
                 'hostId': id, 'name': 'custom.metrics.loadavg',
-                'time': 1401537844, 'value': 1.4
+                'time': 1401537844, 'value': 1.4,
             },
             {
                 'hostId': id, 'name': 'custom.metrics.uptime',
-                'time': 1401537844, 'value': 500
-            }
+                'time': 1401537844, 'value': 500,
+            },
 
         ]
         ret = self.client.post_metrics(metrics)
@@ -137,34 +143,34 @@ def test_should_post_metrics(self, m):
 
     @patch('mackerel.client.requests.post')
     def test_should_post_service_metrics(self, m):
-        """ Client().post_service_metrics() should return success. """
+        """Client().post_service_metrics() should return success."""
         dummy_response(m, 'fixtures/success.json')
         metrics = [
             {
                 'name': 'custom.metrics.latency',
-                'time': 1401537844, 'value': 0.5
+                'time': 1401537844, 'value': 0.5,
             },
             {
                 'name': 'custom.metrics.uptime',
-                'time': 1401537844, 'value': 500
-            }
+                'time': 1401537844, 'value': 500,
+            },
         ]
         ret = self.client.post_service_metrics('service_name', metrics)
         self.assertEqual(ret['success'], True)
 
     @patch('mackerel.client.requests.post')
     def test_should_raise_error_when_service_not_found(self, m):
-        """ Client().post_service_metrics() should raise error when service name not found. """
+        """Client().post_service_metrics() should raise error when service name not found."""
         dummy_response(m, 'fixtures/error.json', 404)
         metrics = [
             {
                 'name': 'custom.metrics.latency',
-                'time': 1401537844, 'value': 0.5
+                'time': 1401537844, 'value': 0.5,
             },
             {
                 'name': 'custom.metrics.uptime',
-                'time': 1401537844, 'value': 500
-            }
+                'time': 1401537844, 'value': 500,
+            },
         ]
         with self.assertRaises(MackerelClientError):
             self.client.post_service_metrics('foobarbaz', metrics)
@@ -179,14 +185,14 @@ def setUpClass(cls):
 
     @patch('mackerel.client.requests.get')
     def test_should_get_ipaddress(self, m):
-        """ Host().ip_addr() should get ipaddress. """
+        """Host().ip_addr() should get ipaddress."""
         dummy_response(m, 'fixtures/get_host.json')
         host = self.client.get_host(self.id)
         self.assertEqual(host.ip_addr(), '10.0.2.15')
 
     @patch('mackerel.client.requests.get')
     def test_should_get_macaddress(self, m):
-        """ Host().mac_addr() should get ipaddress. """
+        """Host().mac_addr() should get ipaddress."""
         dummy_response(m, 'fixtures/get_host.json')
         host = self.client.get_host(self.id)
         self.assertEqual(host.mac_addr(), '08:00:27:96:ed:36')
diff --git a/tox.ini b/tox.ini
index ab35bc0..1b3c5de 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,5 +1,5 @@
 [tox]
-envlist = py27,py36,py37,pycodestyle
+envlist = py27,py36,py37,flake8
 
 [testenv]
 commands=python setup.py test
@@ -8,6 +8,6 @@ deps=
   simplejson
   mock
 
-[testenv:pycodestyle]
-deps = pycodestyle
-commands = pycodestyle --repeat --ignore=E501 --show-source mackerel tests setup.py
+[testenv:flake8]
+deps = flake8
+commands = flake8 mackerel tests setup.py