Abstract: A user authentication system is provided with a client apparatus and an authentication server. An application program used for processing the measurement results of the measuring apparatus is installed on the client apparatus. Databases for storing use authority information of the application program are provided on the authentication server. A user inputs authentication information when operating the client apparatus and the application program is started. The client apparatus sends the authentication information to the authentication server, and an authentication process is performed by the authentication server. When authentication is successful, the use authority information of this user is sent from the authentication server to the client apparatus, and the client apparatus sets the application use restrictions according to the use authority information.