An administration server determines whether a request from a first client terminal is for authentication of a specific user who is in a log-in state via a second client terminal. When the request is for the specific user, the administration server performs a first or a second control, the first control including creating a new password; replacing an old password that is for the specific user to log-in to a network via the second client terminal with the new password; and sending the new password to the first client terminal, and the second control including determining that the request is disapproval; and sending a result of disapproval to the first client terminal. A double-log in by the same user and crush of an individual storage unit caused by a double-log in with the same user ID can be prevented.