PURPOSE: To bind objects with high reliability by providing hole parts near the periphery of either a projecting part of recess and fitting bar materials into said holes and expanding the holes in the case of binding the objects by fitting of the projecting part and the recess.

CONSTITUTION: The 1st core 4 is laminated with plate magnetic bodies 41 and is fixed by rivets. The recess 411 and the holes 412 near the recess are provided to each body 41. Such core 4 and the 2nd core 3 are bound to each other by fitting of the recess 42 and the projecting part. The rivets 27, 28 are inserted into the holes 43 of the core 4 and a pressure is exerted to both ends of the rivets 27, 28 to expand radially the circular sectional parts of the rivets 27, 28, by which the recess 42 is diminished in a manner as to eliminate the space between the hole 42 and the projecting part of the 2nd core and the core 4 and the core 3 are thoroughly bound.