PURPOSE: To prevent frictional wear of an iron core of side leg in process of assembly by arranging an extended supporting member for supporting upper and lower surfaces of side legs on flange of a coil bobbin, which is extended along both sides with the exception of a part being in contact with a laminated thick part of side legs of the iron core body as well as by extending said extended supporting member beyond a width of the side legs of both side of the iron core body.

CONSTITUTION: L-shaped iron core forming two side leg 25 of an iron core body 24 is supported by an extended supporting member 17 of flanges 13 and 14 of a bobbin 11 so that there is not caused frictional wear of the iron core laminated in process of assembly before next process and assembly efficiency increases. A covering member 30 is fastened by a case body 27 and when the covering member 30 and the case body 27 hold a magnetic structure 26, two side leg 25 of the iron core 24 is supported by the extended supporting member 17 of the bobbin 11. Thus the side leg 25 is not bent downwards if it is pushed by the covering member 30 so that there is not produced a slack between the caulked covering member 30 and the iron core body 24 and the covering member 30 can be caulked securely.