If a management server receives an invitation request, the management server acquires a requester's reference identification information corresponding to a requester's user identification information, a receiver's reference identification information corresponding to a receiver's user identification information, and an identification information, by referring to a user information table. The management server generates a record in which a status information is set to “pending”, and records the record in an invitation table. Assuming that the game to which a user A wants to invite another user B is a game b, the other user B who builds a friendship with the user A in a game c, the user A manages one terminal device, and the other user B manages another terminal device. In this case, the management server sends an invitation mail indicating that there is an invitation from the user A in the game b to the other terminal device.