PURPOSE: To easily release the registration of a pass word, and to realize a secrecy holding mechanism whose reliability is high.

CONSTITUTION: When a floppy disk drive 22 is connected at the time of the registration of the pass word, the pass word equal to the pass word registered in a system is stored in the prescribed sector of a key floppy disk 23 set at the floppy disk drive 22. At the time of releasing the registration of the pass word, the key floppy disk 23 is set at the floppy disk drive 22, and the pass word is read from the prescribed sector of the key floppy disk 23. When the read pass word is matched with the pass word registered in the system, the pass word registered in the system and the pass word stored in the key floppy disk 23 are deleted.