To improve convenience for a user who requests login while assuring security nature.

At a preparation stage, a use tendency information generation processing part 11 collects information regarding user's use situation defined by use situation definition information for a fixed period after user authentication, grasps server use tendency of each user by analyzing the information and generates use tendency information by associating authentication levels with each use situation. To a login request transmitted after termination of preparation, an authentication level determination part 12 compares and collates the user's use situation at the point of receiving the login request with the user's use tendency information to determine an authentication level to the login request. A user authentication execution control part 13 performs the user authentication to the login request according to authentication procedures corresponding to the determined authentication level.