A bidding system for receiving bidding by bidders by disclosing bidding information received from a bid inviter, and receiving successful bidder information decided by the inviter based on the bidding information, the system comprising a bid processing unit (14) for receiving bidding amount range information transmitted from bidders via a communication network, and a commission charging unit (13) for calculating commission based on the bidding amount range information received from the bid processing unit (14), a common key being used to prevent information from leaking to a site operator.
