An arc welding apparatus includes a single-electrode type welding torch, a single wire feeder supplied with a plurality of welding wires and having a plurality of wire driving means for driving the plurality of welding wires, and a welding controller for controlling operations of the welding torch and the wire feeder. The welding controller selectively operates any one of the plurality of wire driving means to feed only a single welding wire to the welding torch and performs the arc welding. An arc welding robot system includes the arc welding apparatus, a robot mechanical part for holding the welding torch of the arc welding apparatus, and a robot controller for controlling operation of the robot mechanical part.