Abstract: The invention provides for the disabling of a communication device even when information has been obtained unlawfully which is required for communication, such as unique identification information of a communication device (SID) and a unique identification information of a subscriber (PID).

Abstract: A credit card system has a card with first identification information written thereon, a reading/writing unit for writing information on and reading information from the card, an input device for entering second identification information, a processor for deriving second identification information from information written on the card, comparing the second identification information entered by the entering device with the second identification information derived by the deriving device, and controlling the reading/writing unit to write information representing allowance of issuance of the card on the card if the compared second identification information agrees with each other.

Abstract: A credit card system has a card having at least identification information and management information recorded thereon, a first system for determining whether a credit card can be used or not, and a second system for determining whether the credit card can be used or not. The first system has a communication device for communicating with the second system, a card reader for reading the identification information and the management information recorded on the credit card, and a system processor for determining whether the credit card can be used or not, and judging whether usability of the credit card is to be determined by the first system or the second system based on the management information recorded on the credit card.

Abstract: A credit card system includes a card having storage columns for recording first identification information, a generating unit for generating a check code from the first identification information and second identification information, a card reader/writer for reading information from and writing information on the card, a keyboard for entering the second identification information and a check code. A comparing unit compares the check code generated by the generating means with a check code entered by the keyboard or a check code recorded on the card, and a unit for indicating or displaying information representing that the check codes compared by the comparing unit do not agree with each other if the compared check codes do not agree with each other.