PURPOSE: To surely perform the authorization of a card owner, by storing a telephone number proper to a terminal equipment connected to a center via a communication line on an IC card used in the said terminal equipment, and judging coincidence between the telephone number stored in the IC card and the telephone number proper to the terminal equipment detected at a center side.

CONSTITUTION: The IC card 4 is loaded on the terminal equipment 3. Then, prescribed key data is inputted from a keyboard 36. The telephone number attached on the IC card is sent from a modem 34 for data communication to the computer 11 of the center(bank)1 via a public telephone line with the data such as a bank number, an account number, and a name, etc., required for the balance inquiry of the bank. Then, the computer 11 of the center(bank)1 detects the telephone number of the terminal equipment 3 performing the data communication currently, and decides the coincidence between the telephone number and the telephone number proper to a dedicated terminal equipment sent from the terminal equipment 3 via the modem 34 for the data communication.