To provide a user authentication system which suitably improves convenience by simplifying input operation for authentication information while securing security.

An authentication part 30a sends authentication information auth(b) to an application APb on condition that access control information access(a→;b) in an access control information storage part 42b indicates that actuation is allowed when a request to start the application APb is received next after application APa is started. When receiving the authentication information from the authentication part 30a, the application APb collates whether or not the received authentication information matches the authentication information auth(b) in the authentication information storage part 42f and starts when authenticating their matching.