PURPOSE: To fix unitarily on the core side surface without generating clearances and thus improve the fixing strength, by fusing side projections of a shading coil by plasma welding and welding them on the core surface.

CONSTITUTION: The iron core is formed by lamination-fixing thin pieces in superposition in a plurality by rivets 13. In two groove parts 11 and 11 formed on magnetic pole surfaces 10 and 10, a shading coil 12 in an approx. O-shape is fitted. When the fitting thereof, the side projections 12a and 12a of the shading coil 12 are projected out from the side surface of the core with some clearances. These side projections 12a and 12a are fused by a plasma welding and welded unitarily on the core side surface. This welding is automatically performed by contacting the electrode of a plasma welding machine from both sides on the side projections.