PROBLEM TO BE SOLVED: To eliminate influence of an outer magnetic field without applying any magnetic shield against an electromagnetic coil and without arranging a correcting coil.SOLUTION: There is provided a coil 13 for detecting a composite magnetic field so as to detect an orientation and an intensity of composite magnetic field of a magnetic field (controlling magnetic field) φS generated by an electromagnetic coil 7 and a component φG in parallel with the controlling magnetic field φS of an outer magnetic field acted on the electromagnetic coil 7. A calculation part 1A is provided with a control output correction function F2 so as to correct a control output (coil driving current) Is in such a way that an orientation and an intensity of the composite magnetic field detected by the coil 13 for detecting the composite magnetic field may become the same as an orientation and an intensity of the magnetic field (an object magnetic field) corresponding to a target value to be generated by the electromagnetic coil 7.SELECTED DRAWING: Figure 3
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