An effective means for system authentication by a user. A system is characterized by connecting an electronic apparatus on the system management side to a terminal on the user side via a communication line including the internet and, using system authentication information recorded on a recording medium included in the electronic apparatus on the system side and personal authentication information entered through a personal input operation on a user-operated terminal, for mutual authentication between the user and the electronic apparatus on the system management side that is accessed. In the mutual authentication system between the user and the system, two sets of authentication data are registered: one set is personal authentication data indicating the personal authentication information on the user and other set is server authentication date indicating the system authentication information. The system is characterized in that server side authentication using the server authentication date and user side authentication using authentication data of the user are performed alternatively.