Hi Narunet,
You might want to look into the pure-ftpd
-l puredb:/etc/pureftpd.pdb mode, and then use the pure-pw utility to administer users. This has the advantage that you do not need to create a user account for every user on your ftp.
http://www.pureftpd.org/README.Virtual-Users <-- this URL explains more about Virtual Users on your server.
This is the prefered way of configuring the FTP server in my opinion. If anyone who knows a better way to configure an FTP server is reading this, please PM me :-).
Good luck with the problem,
Target