To maintain the bearing accuracy high and to make it possible to reduce in size a geomagnetic gearing sensor by forming a resist mask by photolithographic technology executed on a resist layer, and precisely laminating and forming a thin film layer.

A lower conductor layer 3 and an upper conductor layer 7 are integrated to form an exciting coil C. A ferromagnetic core K2, upper conductor layer 7, interlayer insulating layer 4, flattened layer 5 and interlayer insulating and flattened layer 6 are so formed in tapered states that the film thicknesses are reduced toward the inner peripheral edge Cin and outer periphery edge Cout. A resist mask is so formed on the resist layer executed with photolithographic technology that the thicknesses are gradually reduced in the same shape as the thin film layers, and etched to make it possible to accurately pattern as desired, and hence the thin film layers of complicated multilayer shape or particularly exciting coil C can be precisely laminated and formed. Accordingly, it can be reduced in size with high accuracy, the geomagnetism is efficiently supplied as a magnetic signal to an MR sensor (magnetoresistance effect element) to obtain the high bearing accuracy.