PURPOSE: To prevent a high temp. crack and to improve the shape of a bead, etc. by arranging the stator of an alternating current linear motor just the above or the below of a molten pool in the laser beam welding that a welding current is not passed to the base metal.

CONSTITUTION: The stator 21 of a cylindrical three phase AC linear motor is arranged at the position just the above or the below of a molten pool 2 in the laser beam welding, etc. which forms the molten pool 2 and melting metal 3 via a laser beam 30 on a base metal 1. The stator 21 is of annular shape, providing a radial projecting part on the lower face and is composed of the core which forms a notch part on one place thereof and a coil 25. A magnetic flux density is formed with the passing of a three phase alternating current to the stator 21, the waveform thereof forms a progressive magnetic field and the molten pool 2 is subjected to a magnetic agitation by the mutual action with the eddy current to be generated in the base metal. In this way, the prevention from high temp. cracks, the improvement of the bead shape and the structural improvement of the welding metal can be performed.