A control unit issues temporary authentication information for disabling a locking/unlocking process to a user terminal satisfying a first condition. The control unit determines whether first authentication information has been issued to another user terminal, issues second authentication information to the user terminal to which the temporary authentication information has been issued when the first authentication information has not been issued to another user terminal, and issues the second authentication information to the user terminal to which the temporary authentication information has been issued with detection of ending of use of the first authentication information in another user terminal as a trigger when the first authentication information has been issued to the other user terminal.