An arc welding system according to the present invention includes a welding power supply for supplying welding power to a welding wire, a welding robot including a welding torch mounted to an arm fore end thereof, and a controller for controlling the welding power supply and the welding robot. The welding power supply and the controller perform communication using digital signals, and the welding power supply outputs, to the controller, a welding power-supply feedback signal obtained at the time of inputting of a welding power-supply sync signal. With that configuration, accurate arc tracking can be realized by using the digital signals.