Can't write UTF-8 Format.

[hanmoai]

Hello,

I just installed emacs for windows version. (emacs-21.3)

Weird thing is that I could type utf-8, but couldn't write it to utf-8
format. When I write it by C-x C-s, I got following messages:

----------
These default coding systems were tried:
  mule-utf-8
However, none of them safely encodes the target text.

Select one of the following safe coding systems:
  euc-kr iso-2022-kr iso-2022-jp-2 x-ctext iso-2022-7bit raw-text
  emacs-mule no-conversion iso-2022-7bit-lock-ss2
  ctext-no-compositions iso-2022-8bit-ss2 iso-2022-7bit-lock
  iso-2022-7bit-ss2 tibetan-iso-8bit-with-esc thai-tis620-with-esc
  lao-with-esc korean-iso-8bit-with-esc hebrew-iso-8bit-with-esc
  greek-iso-8bit-with-esc iso-latin-9-with-esc iso-latin-8-with-esc
  iso-latin-5-with-esc iso-latin-4-with-esc iso-latin-3-with-esc
  iso-latin-2-with-esc iso-latin-1-with-esc
  in-is13194-devanagari-with-esc cyrillic-iso-8bit-with-esc
  chinese-iso-8bit-with-esc japanese-iso-8bit-with-esc
------------

I couldn't find utf-8 in "safe coding systems."

How can I enable utf-8 in the safe coding systems?

Thank you,

Daniel.