When the AJAX calls the php file, I've noticed the data in the $_POST are garbage data.

I think the problem is during GetXmlHttpObject execution to past the Posted data to php file.

Please teach me to set the charset in AJAX supporting Japanese charset.

Currently, I am using the following settings:

PostgreSQL ver 7.4.1 encoding: UNICODE

Javascript/AJAX code:
xmlHttp.setRequestHeader("Content-Type", "application/x-www-form-urlencoded; charset=shift_jis'");
PHP code:
PHP Code:
header('Content-Type: text/html; charset=shift_jis'); 
HTML code:
<meta http-equiv="Content-Type" content="text/html; charset=shift_jis">