From the robot controller, a laser irradiation start command is issued to the laser oscillator, together with a laser power command condition before arc generation. The laser power command before arc generation is used to suppress an amount of heat input, and is selected from among the first to the third laser power commands according to conditions of the material and thickness of base metal and the like. An arc welding start command is issued to the arc welding power source, together with welding voltage and wire feeding speed commands. Before the arc welding command is issued and the wire comes into contact with the base metal, the voltage becomes no-load voltage. Also, the slow wire feeding speed is instructed before the arc is generated. When the wire comes into contact with the base metal and the arc is generated, it is detected and the laser power command condition is changed to a condition for processing.