PURPOSE: To easily form a insulating layer in desired shape without performing an insulating process using an insulating cover or resin, to cut down the cost of production, and to obtain the titled choke coil of small size, light weight and low cost by a method wherein an oxide insulating layer is formed on the whole circumferential surface of a magnetic material, and a coil winding is wound through said oxide insulating layer.

CONSTITUTION: A magnetic material 11 and a coil winding 13 are constituted in such a manner that they are insulated by an oxide insulating layer 12. The oxide insulating layer 12 can be formed easily on the whole circumferential surface of the magnetic material easily by sintering the magnetic material 11 in an air atmosphere without performing an additional process. Also, a more stable oxide film can be obtained by performing a sintering after the magnetic material 11 is dipped in a ferrous oxide aqueous solution in advance. The oxide insulating layer 12 obtained by performing the above-mentioned procedures has sufficient dielectric strength required for a high frequency filter.