PURPOSE: To simplify the winding work and to obtain a small sized choke core manufacturable inexpensively, by providing a short circuit preventing the leakage of magnetic flux from joints between cores, for a closed magnetic circuit consisting of a plurality of cores.

CONSTITUTION: A closed magnetic circuit is constituted with a plurality of cores 2, 3 of closed magnetic circuit constitution, and a magnetic short path consisting of one or a plurality of cores 4, 5 of magnetic short-circuit constitution is provided for this closed magnetic circuit. Windings 6, 7 are wound on the cores 2, 3. Thus, the leakage of magnetic flux from the joints of the cores 2, 3 can be reduced remarkably through the provision of the cores 4, 5. Since the closed magnetic circuit can be assembled with a plurality of cores, the winding work can be simplified much.