diff --git a/Gemfile.lock b/Gemfile.lock
index ee8db6a..b0bbb22 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1,7 +1,7 @@
 PATH
   remote: .
   specs:
-    danger-lgtm (1.0.2)
+    danger-lgtm (1.0.3)
       danger-plugin-api (~> 1.0)
 
 GEM
diff --git a/lib/lgtm/error_handleable.rb b/lib/lgtm/error_handleable.rb
new file mode 100644
index 0000000..1625e31
--- /dev/null
+++ b/lib/lgtm/error_handleable.rb
@@ -0,0 +1,33 @@
+module Lgtm
+  # ErrorHandleable is module of error handling
+  module ErrorHandleable
+    # 4xx http status.
+    CLIENT_ERRORS = [
+      Net::HTTPBadRequest,
+      Net::HTTPForbidden,
+      Net::HTTPNotFound
+    ].freeze
+    # 5xx http status.
+    SERVER_ERRORS = [
+      Net::HTTPInternalServerError,
+      Net::HTTPBadGateway,
+      Net::HTTPServiceUnavailable,
+      Net::HTTPGatewayTimeOut
+    ].freeze
+
+    # validate_response is response validating
+    #
+    # @param [Net::HTTPxxx] response Net::HTTP responses
+    # @raise ::Lgtm::Errors::UnexpectedError
+    # @return [void]
+    #
+    def validate_response(response)
+      case response
+      when *SERVER_ERRORS
+        raise ::Lgtm::Errors::UnexpectedError
+      when *CLIENT_ERRORS
+        raise ::Lgtm::Errors::UnexpectedError
+      end
+    end
+  end
+end
diff --git a/lib/lgtm/errors.rb b/lib/lgtm/errors.rb
new file mode 100644
index 0000000..81158ae
--- /dev/null
+++ b/lib/lgtm/errors.rb
@@ -0,0 +1,6 @@
+module Lgtm
+  class Errors
+    class UnexpectedError < StandardError
+    end
+  end
+end
diff --git a/lib/lgtm/gem_version.rb b/lib/lgtm/gem_version.rb
index 2c6250d..71ffd74 100644
--- a/lib/lgtm/gem_version.rb
+++ b/lib/lgtm/gem_version.rb
@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 module Lgtm
-  VERSION = '1.0.2'.freeze
+  VERSION = '1.0.3'.freeze
 end
diff --git a/lib/lgtm/plugin.rb b/lib/lgtm/plugin.rb
index a5f3bc4..1b3fd29 100644
--- a/lib/lgtm/plugin.rb
+++ b/lib/lgtm/plugin.rb
@@ -3,6 +3,8 @@
 require 'uri'
 require 'json'
 require 'net/http'
+require './lib/lgtm/errors'
+require './lib/lgtm/error_handleable'
 
 module Danger
   # Lgtm let danger say lgtm when there is no violations.
@@ -16,13 +18,14 @@ module Danger
   # @tags lgtm, github
   #
   class DangerLgtm < Plugin
+    include ::Lgtm::ErrorHandleable
     RANDOM_LGTM_POST_URL = 'https://lgtm.in/g'.freeze
 
     # Check status report, say lgtm if no violations
     # Generates a `markdown` of a lgtm image.
     #
-    # @param   [image_url] lgtm image url
-    # @param   [https_image_only] fetching https image only if true
+    # @param  [String] image_url lgtm image url
+    # @param  [Boolean] https_image_only https image only if true
     #
     # @return  [void]
     #
@@ -41,7 +44,6 @@ def check_lgtm(image_url: nil, https_image_only: false)
 
     # returns "<h1 align="center">LGTM</h1>" when ServiceTemporarilyUnavailable.
     def fetch_image_url(https_image_only: false)
-      return unless lgtm_post_url
       lgtm_post_response = process_request(lgtm_post_url) do |req|
         req['Accept'] = 'application/json'
       end
@@ -53,6 +55,7 @@ def fetch_image_url(https_image_only: false)
         return fetch_image_url(https_image_only: true)
       end
       url
+    rescue ::Lgtm::Errors::UnexpectedError; nil
     end
 
     def process_request(url)
@@ -68,9 +71,9 @@ def process_request(url)
     end
 
     def lgtm_post_url
-      lgtm_post_req = process_request(RANDOM_LGTM_POST_URL)
-      return if lgtm_post_req.code == '503'
-      lgtm_post_req['location']
+      res = process_request(RANDOM_LGTM_POST_URL)
+      validate_response(res)
+      res['location']
     end
 
     def markdown_template(image_url)
diff --git a/spec/lgtm_spec.rb b/spec/lgtm_spec.rb
index 889beb2..04f4369 100644
--- a/spec/lgtm_spec.rb
+++ b/spec/lgtm_spec.rb
@@ -2,72 +2,73 @@
 
 require File.expand_path('spec_helper', __dir__)
 
-module Danger
-  describe Danger::DangerLgtm do
-    it 'should be a plugin' do
-      expect(Danger::DangerLgtm.new(nil)).to be_a Danger::Plugin
-    end
-
-    #
-    # You should test your custom attributes and methods here
-    #
-    describe 'with Dangerfile' do
-      before do
-        @dangerfile = testing_dangerfile
-        @lgtm = @dangerfile.lgtm
-      end
+describe Danger::DangerLgtm do
+  def mock(request_url: 'https://lgtm.in/p/sSuI4hm0q',
+           actual_image_url: 'https://example.com/image.jpg')
+    double(
+      :[] => request_url,
+      body: JSON.generate(
+        actualImageUrl: actual_image_url
+      )
+    )
+  end
 
-      # Some examples for writing tests
-      # You should replace these with your own.
+  it 'should be a plugin' do
+    expect(Danger::DangerLgtm.new(nil)).to be_a(Danger::Plugin)
+  end
 
-      it 'lgtm with no violation' do
-        @lgtm.check_lgtm
-        expect(@dangerfile.status_report[:markdowns].length).to eq(1)
-      end
+  describe '#check_lgtm' do
+    subject do
+      lgtm.check_lgtm(
+        https_image_only: https_image_only,
+        image_url: image_url
+      )
+    end
 
-      it 'lgtm with default url is OverQuota' do
-        allow(Net::HTTP).to receive(:start).and_return(mock(code: '503'))
+    let(:dangerfile) { testing_dangerfile }
+    let(:lgtm) { dangerfile.lgtm }
+    let(:https_image_only) { false } # default false
+    let(:image_url) {} # default nil
 
-        @lgtm.check_lgtm
+    shared_examples 'returns correctly message' do
+      it do
+        allow(Net::HTTP).to receive(:start).and_return(mock)
+        is_expected
 
-        expect(@dangerfile.status_report[:markdowns][0].message)
-          .to eq("<h1 align='center'>LGTM</h1>")
+        expect(dangerfile.status_report[:markdowns][0].message)
+          .to match(expected_message)
       end
+    end
 
-      def mock(request_url: 'https://lgtm.in/p/sSuI4hm0q',
-               actual_image_url: 'https://example.com/image.jpg',
-               code: '302')
-        double(
-          :[] => request_url,
-          body: JSON.generate(
-            actualImageUrl: actual_image_url
-          ),
-          code: code
-        )
+    context 'with Dangerfile' do
+      it 'when no violation' do
+        is_expected
+        expect(dangerfile.status_report[:markdowns].length).to eq(1)
       end
 
-      it 'pick random pic from lgtm.in' do
-        allow(Net::HTTP).to receive(:start).and_return(mock)
-
-        @lgtm.check_lgtm
-
-        expect(@dangerfile.status_report[:markdowns][0].message)
-          .to match(%r{https:\/\/example.com\/image.jpg})
+      it 'lgtm with errors' do
+        allow(lgtm).to receive(:validate_response)
+          .and_raise(::Lgtm::Errors::UnexpectedError)
+        is_expected
+        expect(dangerfile.status_report[:markdowns][0].message)
+          .to eq("<h1 align='center'>LGTM</h1>")
       end
 
-      it 'pick random pic from lgtm.in with https_image_only option' do
-        allow(Net::HTTP).to receive(:start).and_return(mock)
-
-        @lgtm.check_lgtm https_image_only: true
+      context 'pick random pic from lgtm.in' do
+        let(:expected_message) { %r{https:\/\/example.com\/image.jpg} }
+        it_behaves_like 'returns correctly message'
+      end
 
-        expect(@dangerfile.status_report[:markdowns][0].message)
-          .to match(%r{https:\/\/example.com\/image.jpg})
+      context 'pick random pic from lgtm.in with https_image_only option' do
+        let(:https_image_only) { true }
+        let(:expected_message) { %r{https:\/\/example.com\/image.jpg} }
+        it_behaves_like 'returns correctly message'
       end
 
-      it 'use given url' do
-        @lgtm.check_lgtm image_url: 'http://imgur.com/Irk2wyX.jpg'
-        expect(@dangerfile.status_report[:markdowns][0].message)
-          .to match(%r{http:\/\/imgur\.com\/Irk2wyX\.jpg})
+      context 'use given url' do
+        let(:image_url) { 'http://imgur.com/Irk2wyX.jpg' }
+        let(:expected_message) { %r{http:\/\/imgur\.com\/Irk2wyX\.jpg} }
+        it_behaves_like 'returns correctly message'
       end
     end
   end