diff --git a/ext/nkf/lib/kconv.rb b/ext/nkf/lib/kconv.rb
index deaa4a02f6..091b88b1c0 100644
--- a/ext/nkf/lib/kconv.rb
+++ b/ext/nkf/lib/kconv.rb
@@ -3,9 +3,17 @@
 #
 # $Id$
 #
+# ----
+#
+# kconv.rb implements the Kconv class for Kanji Converter.  Additionally,
+# some methods in String classes are added to allow easy conversion.
+#
 
 require 'nkf'
 
+#
+# Kanji Converter for Ruby.
+#
 module Kconv
   #
   # Public Constants
@@ -35,7 +43,7 @@ module Kconv
   UTF32 = NKF::UTF32
   # UNKNOWN
   UNKNOWN = NKF::UNKNOWN
-  
+
   #
   # Private Constants
   #
@@ -130,10 +138,11 @@ module Kconv
   # Convert <code>str</code> to ISO-2022-JP
   #
   # *Note*
-  # This method convert halfwidth katakana to fullwidth katakana.
+  # This method decode MIME encoded string and
+  # convert halfwidth katakana to fullwidth katakana.
   # If you don't want it, use NKF.nkf('-jxm0', str).
   def tojis(str)
-    ::NKF::nkf('-jm0', str)
+    ::NKF::nkf('-jm', str)
   end
   module_function :tojis
 
@@ -143,7 +152,8 @@ module Kconv
   # Convert <code>str</code> to EUC-JP
   #
   # *Note*
-  # This method convert halfwidth katakana to fullwidth katakana.
+  # This method decode MIME encoded string and
+  # convert halfwidth katakana to fullwidth katakana.
   # If you don't want it, use NKF.nkf('-exm0', str).
   def toeuc(str)
     ::NKF::nkf('-em0', str)
@@ -156,10 +166,11 @@ module Kconv
   # Convert <code>str</code> to Shift_JIS
   #
   # *Note*
-  # This method convert halfwidth katakana to fullwidth katakana.
+  # This method decode MIME encoded string and
+  # convert halfwidth katakana to fullwidth katakana.
   # If you don't want it, use NKF.nkf('-sxm0', str).
   def tosjis(str)
-    ::NKF::nkf('-sm0', str)
+    ::NKF::nkf('-sm', str)
   end
   module_function :tosjis
 
@@ -169,10 +180,11 @@ module Kconv
   # Convert <code>str</code> to UTF-8
   #
   # *Note*
-  # This method convert halfwidth katakana to fullwidth katakana.
+  # This method decode MIME encoded string and
+  # convert halfwidth katakana to fullwidth katakana.
   # If you don't want it, use NKF.nkf('-wxm0', str).
   def toutf8(str)
-    ::NKF::nkf('-wm0', str)
+    ::NKF::nkf('-wm', str)
   end
   module_function :toutf8
 
@@ -182,10 +194,11 @@ module Kconv
   # Convert <code>str</code> to UTF-16
   #
   # *Note*
-  # This method convert halfwidth katakana to fullwidth katakana.
+  # This method decode MIME encoded string and
+  # convert halfwidth katakana to fullwidth katakana.
   # If you don't want it, use NKF.nkf('-w16xm0', str).
   def toutf16(str)
-    ::NKF::nkf('-w16m0', str)
+    ::NKF::nkf('-w16m', str)
   end
   module_function :toutf16
 
@@ -258,7 +271,8 @@ class String
   # <code>out_code</code> and <code>in_code</code> are given as constants of Kconv.
   #
   # *Note*
-  # This method convert halfwidth katakana to fullwidth katakana.
+  # This method decode MIME encoded string and
+  # convert halfwidth katakana to fullwidth katakana.
   # If you don't want to decode them, use NKF.nkf.
   def kconv(out_code, in_code=Kconv::AUTO)
     Kconv::kconv(self, out_code, in_code)
@@ -274,7 +288,8 @@ class String
   # Convert <code>self</code> to ISO-2022-JP
   #
   # *Note*
-  # This method convert halfwidth katakana to fullwidth katakana.
+  # This method decode MIME encoded string and
+  # convert halfwidth katakana to fullwidth katakana.
   # If you don't want it, use NKF.nkf('-jxm0', str).
   def tojis; Kconv.tojis(self) end
 
@@ -284,7 +299,8 @@ class String
   # Convert <code>self</code> to EUC-JP
   #
   # *Note*
-  # This method convert halfwidth katakana to fullwidth katakana.
+  # This method decode MIME encoded string and
+  # convert halfwidth katakana to fullwidth katakana.
   # If you don't want it, use NKF.nkf('-exm0', str).
   def toeuc; Kconv.toeuc(self) end
 
@@ -294,7 +310,8 @@ class String
   # Convert <code>self</code> to Shift_JIS
   #
   # *Note*
-  # This method convert halfwidth katakana to fullwidth katakana.
+  # This method decode MIME encoded string and
+  # convert halfwidth katakana to fullwidth katakana.
   # If you don't want it, use NKF.nkf('-sxm0', str).
   def tosjis; Kconv.tosjis(self) end
 
@@ -304,7 +321,8 @@ class String
   # Convert <code>self</code> to UTF-8
   #
   # *Note*
-  # This method convert halfwidth katakana to fullwidth katakana.
+  # This method decode MIME encoded string and
+  # convert halfwidth katakana to fullwidth katakana.
   # If you don't want it, use NKF.nkf('-wxm0', str).
   def toutf8; Kconv.toutf8(self) end
 
@@ -314,7 +332,8 @@ class String
   # Convert <code>self</code> to UTF-16
   #
   # *Note*
-  # This method convert halfwidth katakana to fullwidth katakana.
+  # This method decode MIME encoded string and
+  # convert halfwidth katakana to fullwidth katakana.
   # If you don't want it, use NKF.nkf('-w16xm0', str).
   def toutf16; Kconv.toutf16(self) end