To provide commodity purchasing method and system improving economical efficiency and safety for the purchase of a commodity by a credit transaction or account payment transaction utilizing a network such as the Internet and improving convenience for the purchase of a commodity by a prepaid transaction.

When a user requiring the purchase of a commodity by using the network inputs prescribed transaction data to a prescribed home page and directly transmits prescribed certification data to a credit company or a financial institution through a credit finance information system (CAFIS) network without passing it through a third person, a commodity selling agency receives a transaction certification answer transmitted from the credit company or the financial institution through the CAFIS network and executes the transaction in accordance with the propriety of the result to purchase the commodity.