To judge whether or not a control command is normally transmitted while ensuring a unidirectional communication from a main control means to a subsidiary control means.

A command group which is transmitted from a main control section 200 is transmitted to a special pattern display device 100 by a unidirectional communication. At the same time, the command group is returned to the main control section 200 side as well, and whether or not the control command group is normally transmitted can be judged while ensuring the unidirectional communication from the main control section 200 to the special pattern display device 100. Especially, the main control section 200 checks the compatibility between the returned control command group and the command group precedingly transmitted by the main control section 200 itself, and whether or not the command group transmitted to the special pattern display device 100 by the main control section 200 is normal one can be judged.