PURPOSE: To form a magnetic card input/output device in one system by aggregating the function of an ID card and that of a prepaid card in one kind of magnetic card and to dispense with a customer book file retrieved by the customer number of the ID card by recording customer authorization information and purchase information in the magnetic card.
CONSTITUTION: This device is equipped with a magnetic card reader/ writer 3 which performs the read/write of information on the magnetic card 1 on the back plane of which information 7 to authorize a customer, information 8 relating to the purchase of the customer, and prepaid amount payment information 9 are recorded on the back plane and on the surface of which customer information is printed, and also, prints the information on a card surface, and a processing part 2 which performs the addition processing of purchase amount of the card by the purchase of the customer and the subtraction processing of card prepaid amount balance, etc.