PURPOSE: To reduce curvature of an electrode to improve the accuracy of assembly by welding an end electrode and pins with laser beam, and thereafter, melting a part between both the pins from the back of the electrode with laser beam.

CONSTITUTION: Pins 8 are made to abut on an end electrode 5d, and laser beam 11 is made to enter for welding. At this stage, a difference of thermal shrinkage is generated between the surface of incidence of the laser beam and the back surface of the end electrode 5d with the influence of a difference of melted volume, and curvature is generated between the pins 8. Under he condition that curvature is generated, laser beams 12 is made to enter from the back of the incidence side of the laser beam 12, which is made to enter at the time of welding, to melt a part of the end electrode 5d. Curvature is thereby eliminated between the pins 8.