The present invention is to perform authentication to enable linkage among a plurality of different applications providing a service. For example, an authentication server of an embodiment of the present invention is an authentication sever shared among a plurality of different applications providing a service by using the WWW, which is configured to perform user authentication in response to a request from one of the applications, to determine whether an authentication ID associated with a user who succeeded in the authentication is stored in an authentication database, which stores an authentication ID and user's status-of-use information associated with each other, if the authentication succeeded, and to inform the application, which requested for the user authentication, of user's status-of-use information associated with the stored authentication ID to cause the application to perform a process according to the status-of-use information, if the authentication ID associated with the user is determined to be stored.