A signature generation apparatus preventing an transcript attack on signature data. The signature generation apparatus for generating signature data for message data (i) acquires, according to a predetermined acquisition method, a private key, which is different from a private key used in a previous digital signature operation, from among a plurality of private keys generated using a key generation method of a signature scheme in which the plurality of private keys correspond to a single public key, and (ii) performs, using the acquired private key, a digital signature operation on the message data according to a signature method of the signature scheme to generate the signature data.