PURPOSE: To suppress deformations and displacements in welding and to execute the high precision welding by welding by means of laser beam irradiation after the 2nd workpiece to be welded pressed against the 1st workpiece to be welded at a fixed position.

CONSTITUTION: The 2nd plate workpiece 2 smaller in size than the workpiece 1 and same shape as the workpiece 1 is put against the flat plane of the 1st workpiece 1 at a fixed position. The pressing pins 3 of four in number are placed symmetrically against the flat plane of the 2nd workpiece 2. These four pressing pins are free in movement in three-dimensional directions against the flat plane of the workpieces 1 and 2 with the supporting mechanism 4. Laser beams L1WL4 split from a single laser beam are irradiated simultaneously with equal intensity on the welding spots adjacent to each of the pressing pins 3, and welding is executed.