Abstract: The user (10) uses an information terminal (200) having a user authentication application program according to the present invention installed thereon and also uses a user authentication system according to the present invention via the user authentication application program, so that it is authenticated that the user who has registered, in advance, his/her biological information (700) in at least one of the information terminal (200) and an authentication server (300) is/was present at the authentication location during the authentication reception time.