There is provided a technique that enables a process to be performed smoothly between two processing units of an OLT after rebooting of one of the processing units even in the case where a process by the processing unit is temporarily halted. An upper processing unit can be temporarily halted when updating firmware. A basic communication unit (lower processing unit) is configured to maintain its operation even when the upper processing unit is temporarily halted. When an event occurs during a halt period of the upper processing unit, a matching unit matches a management state stored in a first storage unit with a management state stored in a second storage unit after the halt period of the upper processing unit.