To provide an electronic bidding system that is highly transparent in bid opening.

When a secret key is input into a bid price decrypting part 13 to decrypt bid prices stored in a bid price storing part 12 after encrypted with a public key, a winning bidder deciding part 14 substantially simultaneously decides a winning bidder. Further substantially simultaneously, an electronic mail preparing part 15 prepares an electronic mad containing the bidding result, and an electronic mail sending part 16 transmits the electronic mail to a proposer client 20, bidder clients 20 and an auditor client 40 to open the bidding result.