A YAG pulse laser oscillator 10 oscillates/outputs pulse width-variable YAG fundamental pulse laser light LB, and a YAG pulse laser oscillator 12 oscillates/outputs pulse width-variable YAG second harmonic pulse laser light SHG. An emission unit 20 superposes the pulse laser light LB and the pulse laser light SHG on the same optical axis and focuses, and irradiates a welding point K on welding pieces (W1 and W2) with, the pulse laser light LB and the pulse laser light SHG. A control unit 18 controls the laser oscillation operation of the laser oscillators 10 and 12 so that the point in time when the laser output of the YAG second harmonic pulse laser light SHG reaches its peak is slightly earlier than the point in time when the laser output of the YAG fundamental pulse laser light LB reaches its peak.