An interface board includes a synchronizer that synchronizes a first time that is a time of the interface board to a base time based on a master synchronization signal that is supplied by an external master time source and that defines the base time. The interface board also includes a comparator that compares a phase of a first synchronization signal that synchronizes to the first time with a phase of a shared synchronization signal sent by an interface controller that controls the interface board, and a notifier that notifies another interface board of a comparison result of the comparator.