Hi,

Finally, I know what is the problem. Thank you guys for helping this issues.

I am not expert on encoding system, though, I thank this opportunity for me to learn it.

The problem is BOM (Byte Order Mark). In case of utf-8, it is avoided since BOM header could cause conflict when the expected special character is starting position like ‘#!’ in Unix shell script. Therefore, if there is no text written at least 8-bits to be represented in utf-8, the text encoding is not defined or ASCII (I am not sure if it is right term, but here, let’s say it is ASCII for convenience.) in emacs.

I could conclude emacs does not have the feature of having BOM in utf-8. It only supports utf-8 without BOM. So, I could understand why the text was not written in utf-8 if the text does not contain actual utf-8 characters. If there is a text in utf-8 character and save it as utf-8, then there is no problem in writing utf-8 without BOM.

Detailed information about unicode and BOM is found in http://unicode.org/faq/utf_bom.html

Thank you,