, the laser beam L is divided and introduced into the welding robots 12a, 12b by the beam splitter 36, and the supply of the laser beam L to the welding robots 12a, 12b is selectively controlled for independently controlling the welding robots 12a, 12b to weld a plurality of regions in the workpiece W. As a consequence, the period of time required to manufacture a product, such as an automobile, o