PURPOSE: To perform positioning of a path-core accurately and easily by a method wherein a space is provided outside of one of flanges of each coil bobbin by a circular wall protruding perpendicular to the flange and a path-core is, partially or totally, housed in this space.

CONSTITUTION: On the outside of a flange 6 of each coil bobbin 3 which faces each other a continuous circular wall 8, which is perpendicular to the flange 6 and protrudes to the outward direction of the axis, is provided to form a pocket for a path-core 7. When the bobbins 3 are butted, these perpendicular walls 8 form a space in which the path-core 7 is housed partially or totally. With this constitution, the path-core 7 bound from all directions by the perpendicular walls 8 and the outside of the flange 6 so that the positioning is made accurately. The positioning is made by simple fitting the path-core 7 into the pocket in the assembling process so that the assembly becomes extremely easy.