A control system includes a load including an operative part, and a control device for supplying AC power to the load through a power line and operating the operative part. The control device includes an interruption mechanism and a transmission mechanism. The load includes a controller. The transmission mechanism transmits a predetermined control signal to the load through the power line by blocking the power supply to the load by the interruption mechanism for a time duration shorter than a half cycle of AC output. The controller controls the operative part based on the control signal received from the control device.