To support commodity transaction and effectively advertise.

A commodity provision part 35 provides a commodity to a user via network. A sponsor provision part 36 provides a sponsor attaching an advertisement to the commodity by relating to the commodity. When the user agrees the attachment of the advertisement by the sponsor, a discount provision part 38 presents an amount born by the sponsor instead of the user. When the user purchases the commodity, a purchase reception part 42 asks whether or not the user agrees the attachment of the advertisement by the sponsor to the commodity.