A response transmission unit transmits a response including unique information unique to a user who is authenticated on the basis of user identification information, to a session management server, in a case where the user identification information is included in a request received by a reception unit. A transmission unit transmits the response to a client apparatus along with identification information of a service providing server which is a transmission source of the response when the response with the unique information is received. A request transmission unit, in principle, transmits a request received by a request reception unit to a service providing server corresponding to identification information in the request, but transmits a request to a service providing server corresponding to identification information associated with unique information when receiving the request including the same unique information as unique information which has been stored in a session management DB.