When a controlled device receives a change command from a control device, the controlled device changes a real current memory, generates a change notification that includes first data indicative of the control device having transmitted the change command and second data indicative of the change result in response to the change command, and transmits the generated change notification to the plurality of control devices. Each control device receives a change notification from the controlled devices, changes a virtual current memory based on the second data of the change notification if the first data of the change notification does not indicate the control device. Each control device does not change the virtual current based on the second data included in the change notification if the first data indicates the control device.