Protection of an authentication password stored in a database held by a SAM of Windows® is strengthened. A GINA, a part of the OS, receives an authentication password in ASCII codes. The authentication password is converted to first UNICODES, and the first UNICODES are salted with a random number and converted to second UNICODES. The random number used for salting is associated with a user account and a password and stored in a read/write protected non-volatile memory or a non-volatile memory which can be accessed only by a BIOS. An LSA of the OS can process UNICODES without being changed.