Since nickel-coated steel is widely used to prevent rust, it is used in large rolled steel plates in paper mills. It is necessary to inspect the thickness of the nickel layer on nickel-coated steel in the production process to guarantee quality. Moreover, in a real plant, the inspection of the nickel layer on the opposite side of a rolled steel plate is required. The conductivity of the nickel layer in the nickel-coated steel plate is higher than that of the mother steel, and its permeability is lower than that of the mother steel. Therefore, the thickness of the nickel layer can be estimated on the basis of the differences in these electromagnetic properties. In this paper, an electromagnetic inspection method for measuring the thickness of the nickel layer on the opposite side using a pulsed magnetic field is proposed. The detailed phenomenon of the inspection method is examined by the 3D nonlinear finite element method (FEM) considering the hysteresis magnetization curves of both nickel and the mother steel plate. It is shown that the electromagnetic inspection of the thickness of the nickel layer is possible by using the output voltage of a search coil of the proposed sensor.