Certifying system and transaction system with the certification

An optional information supplied from an authenticating equipment (1) or an agreement settled between an equipment (5) to be authenticated and the authenticating equipment is stored in a tamper-proof region in the data stored in the equipment to be authenticated during a predetermined period. A return data including the optional information, a data based on the optional information, or the data based on the agreement are supplied from the equipment to be authenticated to the authenticating equipment. Thereby a rightful user is authenticated, and a network usable by the rightful user based on the authentication is established, so that a suitable authentication and an exclusive single goods or services transaction can be executed.