A mobile communication system includes an association requesting unit provided in a base station and configured to request a base station controller, which is an upper node, to associate the base station with a tracking area; and a state control unit provided in the base station controller and configured to monitor entry or appearance and exit or disappearance of mobile stations in and from the tracking area associated with the base station, to cause the base station to transition to a serving state if at least one of the mobile stations enters or appears in the tracking area, and to cause the base station to transition to a radio-unit-inactive state if all of the mobile stations exit or disappear from the tracking area.