diff --git a/wc.rb b/wc.rb
index 25aef9d..f0a3474 100644
--- a/wc.rb
+++ b/wc.rb
@@ -10,7 +10,7 @@ def parse_options
     opts.on('-c') { options[:bytes] = true }
   end.parse!
   options = { bytes: true, lines: true, words: true } if options.empty?
-  [options, ARGV.empty? ? [ARGF] : ARGV]
+  [options, ARGV.empty? ? ['-'] : ARGV]
 end
 
 def count_file_stats(input)
@@ -24,13 +24,12 @@ def count_file_stats(input)
 end
 
 def process_input(source)
-  if source == ARGF || File.exist?(source)
-    input = source == ARGF ? ARGF.read : File.read(source)
-    count_file_stats(input)
-  else
-    puts "wc: #{source}: そのようなファイルやディレクトリはありません"
-    exit
-  end
+  input = if source == '-'
+            $stdin.read
+          else
+            File.read(source)
+          end
+  count_file_stats(input)
 end
 
 def update_totals(totals, stats)
@@ -50,7 +49,7 @@ def format_result(stats, max_widths, options)
 end
 
 def print_result(result, source)
-  puts "#{result} #{source == ARGF ? '' : source}"
+  puts "#{result} #{source == '-' ? '' : source}"
 end
 
 def print_total(total_stats, max_widths, options)