There is proposed a competitive buying and selling system that avoids unnatural bidding prices and exclusive possession of resources, stabilizes bidding prices, and provides such an environment that participants can bid easily. There are included a first step in which a server opens a subject of buying and selling and a successful bid evaluation function thereof to a plurality of clients, a second step in which each of the clients makes a participant determine the subject of buying and selling and a bidding price thereof by using the successful bid evaluation function, and notifies a determined result to the server, and a third step in which the server selects a bidding price of a participant who has indicated a highest evaluation value based on the successful bid evaluation function among all bidding prices notified from the clients and designates the participant as a successful bidder. The successful bid evaluation function is based on past bidding prices per unit volume and utilization efficiencies of resources knocked down in past. Furthermore, the successful bid evaluation function is based further on a resource occupation rate in bidding of this time.