To prevent joint strength from deteriorating by suppressing the formation of a crater with excessive depth more than before in the end of a welding bead.

A linear pre-processing welding bead 310 is formed in part of a region of a welding scheduled place by scanning a laser beam in a direction from one end side to the other end side of the welding scheduled place. Then, by scanning the laser beam in a direction from the other end side to the one end side of the welding scheduled place, a linear final welding bead 320 is formed in a region from the other end side to the one end side of the welding scheduled place. At this time, an overlapping margin L_L is set to 8 mm or more. An overrun length L_O is set within ±2 mm.