PURPOSE: To improve reliability and speed up the system by controlling a pair of printing supply devices by means of a common control unit, providing means for judging whether the other printing supply device is stopped or not, to the respective printing supply devices, and controlling them so that both the devices are alternately driven when both of them are not stopped, and one of the devices is successively driven when the ther is stopped.

CONSTITUTION: Two printing supply devices 2,2 having respective means 4 for judging whether the other printing supply device is stopped or not, are connected to a common control unit 6. The respective printing supply devices 2 judge whether the other printing supply device 2 is stopped or not by means of their judging means 4, and when the other device is stopped, one being not stopped is successively driven. When both the devices are driven, the devices are controlled to be driven alternately. In this constitution, reliability is improved and the system can be speeded up.