PURPOSE: To determine the position of the wire slot in a core correctly, by providing a cutout portion in the flange of the core, and making the mounting to and dismounting from a winding machine easy.

CONSTITUTION: A hole 5b of a flange 1c of a ferrite core 1 and a hole 6 of a main core portion 1a are coupled with shafts 7a and 7b of a stepped guide pin 7 of a jig 10, respectively. A cutout portion 3 for positioning the flange 1c is coupled with a pin 9. The shaft 7a is embeded in the thickness of the flange 1c and the pin 9 is also embeded in the thickness of the flange 1c. The ferrite core 1 is attracted to and held by the jig 10 by magnets 8a and 8b. The leading portion 2a of a coil 2 is put into the wire slot 4 of the core 1 and the winding is made around the main portion 1a; and the end of the winding 2b is separated from the flange 1c, bent in the direction opposite to the main portion 1a, and formed. Then, the both ends of the wire are cut so that they have the same length. In this constitution, since the core can be readily attached to or detached from the jig, and the position of the wire slot can be correctly determined, the mechanization can be realized to the large extent.