PURPOSE: To reduce noise caused by external magnetism by shielding the magnetism of an element coil and a nearbycore to the outside while covering the element coil with a magnetic shielding body.

CONSTITUTION: A magnetic shielding body 15 is constituted while besecting it to right and left arranging almost semicircularly formed magnetic shielding body constituting members 16 and 16 at a suitable interval with cores 6 and 10 so as to hot it there between. An interval l1 between those both magnetic shield body constituting members 16 and 16 is set wider than intervals l2 and l3 between the magnetic shield body constituting members 16 and the body and head parts of the cores 6 and 10. Since the magnetic shielding body 15 is provided so as to cover a head element 3 and an element coil 9, the element coil 9 or the like can be magnetically shielded to the external space and since the noise caused by an external magnetic field can be reduced, an S/N is im proved.