PURPOSE: To improve the accuracy of a lap joint shape and to increase a welding area in the case of tight laser beam welding of sinks, fuel tanks for automobiles, etc.

CONSTITUTION: The joint parts of members to be welded are powerfully clamped and are welded by irradiating the joint parts with a laser beam 6 from an extension line 5 of the contact surfaces of the clamped and superposed welded joint parts or a line having a slight angle with this extension line 5 in the case of welding of the joint parts of metallic plates 1, 2 superposed on each other by the laser beam. The gap between the plates of the lap joint parts is thus eliminated. Since the extremely marginal point of the weld line is clamped, the distortion at the time of welding is suppressed and dislocation is prevented. Since penetration is possible broadly in the extension line direction of the contact surfaces of the lap joint parts, the welding strength is additionally enhanced.