PURPOSE: To decrease noise and magnetization of a core, by electrically connecting the magnetic core and a shield case.

CONSTITUTION: A pair of magnetic cores 11, 11 are butted together and they are contained in a shield case 15 made of permalloy together with a core support 12. A coil 13 is wound at the rear part of the cores 11 and the ends are connected to terminals 14a and 14b. The rear part of the cores 11 is provided with a projection 11a which is inserted into the core support 12, contacts with the shield case 15 and electrically conducts the cores 11 and the shield case 15. Thus, electric conduction between the magnetic cores and the shield case can be performed surely.