The coding function section in the bidder sub-system 100 is supplied with a code parameter depending on the bidding price, and the bidding price is coded depending on this code parameter. The tender opening system 200 decodes sequentially the decode parameter corresponding to the highest bidding price starting from the highest or the lowest one among bidding prices that can possibly be accepted, and the one that is successfully decoded is judged to be a bidding price corresponding to that parameter and accepted as contract price. The information of unaccepted bidding prices will be concealed, by not publishing the decode parameter concerning the bidding prices of the order inferior to the contract price.