diff --git a/app/models/concerns/fluentd/setting_archive/archivable.rb b/app/models/concerns/fluentd/setting_archive/archivable.rb
new file mode 100644
index 0000000..db34798
--- /dev/null
+++ b/app/models/concerns/fluentd/setting_archive/archivable.rb
@@ -0,0 +1,36 @@
+class Fluentd
+  module SettingArchive
+    module Archivable
+      attr_accessor :file_path
+
+      def file_id
+        @file_id ||= with_file { name.gsub(/#{self.class::FILE_EXTENSION}\Z/,'') }
+      end
+
+      def name
+        @name ||= with_file { File.basename(file_path) }
+      end
+
+      def content
+        @content ||= with_file { File.open(file_path, "r") { |f| f.read } }
+      end
+
+      def ctime
+        with_file { File.ctime(file_path) }
+      end
+
+      private
+
+      def file_path_of(dir, id)
+        file_path = Pathname.new(dir).join("#{id}#{self.class::FILE_EXTENSION}")
+        raise "No such a file #{file_path}" unless File.exist?(file_path)
+        file_path
+      end
+
+      def with_file
+        return nil unless file_path && File.exist?(file_path)
+        yield
+      end
+    end
+  end
+end
diff --git a/app/models/fluentd/setting_archive/backup_file.rb b/app/models/fluentd/setting_archive/backup_file.rb
index 6ee72a7..3b0e2cb 100644
--- a/app/models/fluentd/setting_archive/backup_file.rb
+++ b/app/models/fluentd/setting_archive/backup_file.rb
@@ -1,41 +1,17 @@
 class Fluentd
   module SettingArchive
     class BackupFile
-      attr_accessor :file_path
+      include Archivable
+
+      FILE_EXTENSION = ".conf".freeze
 
       def self.find_by_file_id(backup_dir, file_id)
-        file_path = Pathname.new(backup_dir).join("#{file_id}.conf")
-        raise "No such a file #{file_path}" unless File.exist?(file_path)
-
-        new(file_path)
+        new(file_path_of(backup_dir, file_id))
       end
 
       def initialize(file_path)
         @file_path = file_path
       end
-
-      def file_id
-        @file_id ||= with_file { name.gsub(/.conf\Z/,'') }
-      end
-
-      def name
-        @name ||= with_file { File.basename(file_path) }
-      end
-
-      def content
-        @content ||= with_file { File.open(file_path, "r") { |f| f.read } }
-      end
-
-      def ctime
-        with_file { File.ctime(file_path) }
-      end
-
-      private
-
-      def with_file
-        return nil unless file_path && File.exist?(file_path)
-        yield
-      end
     end
   end
 end