To prevent illicit use of a credit card by adding a simple method to a current system.

The owner of a credit card (hereinafter referred to as the card) registers a normally used mobile telephone number at a card management company, together with personal information. When adjustment with the card is requested, a person in charge of adjustment in a store dealing with the card temporarily keeps the mobile telephone and the card from a card user and inquires about the card via a terminal machine of this store connected to a card management company online and dials the mobile telephone number of the card owner transmitted from the card management company together with personal data, to call the mobile telephone from another telephone and collates the mobile telephone of the card user with that of the card owner. When they match, it is so discriminated that the card user and the card owner as the same person and normal card adjustment procedures are conducted and returns the card and the mobile telephone to the user. If they do not match, settlement by card is rejected.