PURPOSE: To prevent the dielectric breakdown of an insulated layer provided between an upper magnetic layer and a spiral conductor by forming a pierced hole at a connection part reaching a substrate and filling this hole with a conductive material.

CONSTITUTION: A contact state is secured at a connection part 13ab between a part of a 1st magnetic layer 13a formed on a conductive substrate 11 via an insulated film 12 end a part of a 2nd magnetic layer 13b formed on an insulated layer 15 including 8 spiral conductor 14 serving as an electric coil. A pierced hole 21 is drilled through the part 13ab up to the substrate 11. Then the hole 21 is filled with a conductive material 22. Therefore the static electricity charged both layers 13a and 13b is also scattered to the substrate 11. Thus the electric charge applied to both layers 13a and 13b is reduced compared with the quantity of static electricity secured by a conventional system. Then the field intensity is reduced between both layers 13e/13b end the conductor 14 and the dielectric breakdown of the layer 15 can be prevented.