By performing initial user registration via an SSL-compliant browser in an information home electric appliance 100, user's private key, digital certificate, and member information are downloaded (b2) into the storage device in the information home electric appliance. At card use time, when the user selects products on a merchant's SSL-compliant server and issues a purchase instruction (c1), the user is identified locally in the information home electric appliance based on a personal identification number. Subsequently, the information home electric appliance accesses an SSL-compliant settlement server 220 (C4) and sends a digital certificate and member information stored in the appliance. Then, mutual authentication is performed between the user and the settlement server and, based on the member information, an authorization gateway 241 authorizes the account settlement (c5). This allows even an information home electric appliance with a relatively small capacity memory device to conduct relatively secure transactions over the Internet using a credit card.