A secret information server 300 on a network 10 and a client apparatus 100 constitute an authentication information generating system. The secret information server 300 has a function to confirm the validity of a user in accordance with user identification information received from the client apparatus 100 and a function to hold the secret information database of each user and to send the secret information database of a user whose validity has been confirmed to the client apparatus 100 of the user. The client apparatus 100 has a main memory 120 having a domain A where an application or a main OS is executed and a domain B which has a program execution environment mutually independent of that for the domain A. The secret information database received from the secret information server 300 is saved in the domain B, and authentication information is generated by using the secret information database. Secret information required to generate the authentication information for user authentication is held securely at low cost.