To solve the problem in transaction through a personal computer or the like in a network environment such as the Internet or i-mode, that since there is no method for ensuring that the transaction is performed between same persons, identification in the real society by mutually presenting personal information is needed for the transaction, which frequently discloses unnecessary information.

A physical medium such as an IC card and an authentication server registering personal information are used on a network, whereby a reliable anonymous commodity selling and buying system through the network is provided. A commodity carrier and a price intermediate agent which are identified are interposed in the authentication server registering the personal information, whereby payment of the price of a purchased commodity and delivery of the commodity can be performed without disclosing unnecessary personal information or addresses of the seller of the commodity and the purchaser of the commodity.