A schedule data acquisition requestor requests and acquires schedule data from a sub controller. When a modification to the acquired schedule data is made, a schedule data update requestor sends the modified schedule data to the sub controller and requests an update. A schedule data update processor sends a permission notification to a main controller in response to the update request and writes the modified schedule data onto its own flash memory. Conversely, when a rejection notification is sent from the sub controller, the schedule data update requestor displays a warning message and new schedule data on a screen.