A signature log storing apparatus includes a signature log list and a certificate list, and registers, in the signature log list, a part of signature information in generated hysteresis signature as a signature record and a part of a user certificate in the certificate list. The signature log storing apparatus further includes a trust point list and validates a signature records registered in the signature log list and registers identification information for identifying a latest signature record out of the validate signature record, evidence information for validating validity of the user certificate for a validated signature record, and a hash value of information derived by connecting the evidence information and the hash value as needed or before the user certificate expires.