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Since high-speed examination is possible using an electromagnetic nondestructive inspection method, the inspection of an opposite side defect of the tank in the petrochemical plant, etc. by the electromagnetic method is investigated. In this paper, the electromagnetic inspection method using a dc magnetic field and a minute ac magnetic field is proposed. The behavior of flux in steel is examined using a 3-D finite-element method taking into account hysteresis (minor loop) and eddy current. It is shown that the detection of the opposite-side defect is possible with the differential permeability of a minor loop of which the position on the hysteresis loop is affected by the existence of defect.