To provide a personal identification method in electronic commercial transaction using the Internet capable of confirming that a customer in the person himself (herself) by the fact that any number issued by a credit agency and any number inputted by a customer match with each other, and being surer and having no trouble.

In this method, a credit agency issues an optional number to the customer, and the number are sent from the customer to the agency, then personal identification is performed by the fact that the optional number sent to the agency match with the number issued previously by the agency.