PURPOSE: To make impossible the forgery of an IC card, to prevent an improper use even when it is stolen, and to improve security by collating a password number specified for its owner at an IC card side, and checking it at a reader/ writer side only when they coincide.

CONSTITUTION: When the collating process operation of an IC card 1 is started, the presenter of the card 1, first of all, inputs the password number to the reader/writer. Next, at the card 1 side, the password number stored in a ROM within a microcomputer 5 is read out to a CPU, and a collating between the password number sent from the reader/writer is performed. As a result, it is decided that the presenter of the card 1 is its owner only when they coincide, and a result is outputted after a prescribed arithmetic process is applied on the password number. And at the reader/writer side, the collating between the password number sent from the IC card and the password number inputted by a card presenter is performed, and when coincidence between them is obtained, the information to permit the usage of the card is outputted. In this way, the forgery of the card is impossible, and the improper use of the card can be prevented even when it is stolen, thereby the security is improved.