Abstract: When logging in a server via an information network, high security is ensured without using a password. When a terminal 2 accesses a server 3, a random key is sent from the server 3. An operator inputs a fingerprint from an individual identification input device, and the terminal 2 collates the fingerprint information with registered fingerprint information previously registered. If a match is obtained, the terminal 2 generates a log-in packet, and transmits the log-in packet to the server 3. If a match is not obtained, the log-in processing is suspended. The server 3 resolves the received log-in packet, takes out the registered fingerprint information, fingerprint information, and a user code, and collates the registered fingerprint information with fingerprint information. If a match is obtained, the server 3 collates the transmitted user code with a user code previously stored in the server 3. If a match is not obtained, the log-in processing is suspended.