Prior to authentication, a business system generates a password list and sends the password list to a commercial service system. A request for use of the commercial service system is sent from a terminal that a user is using to the business system. In response to this, the business system that received the request for use checks the request for use of a commercial service use authority of the user. A password is selected from the password list and returned to the terminal. The terminal sends the returned password to the commercial service system. The commercial service system compares the password with a password in accounting information including the password list. If they match, login is permitted and the used password is nullified.