Coil is made to be disposed with gap opposed to the surface of wafer, and wafer stage is made to move in X and Y direction and R and θ direction. When supplying an alternating current to coil with the frequency swept by impedance analyzer, the magnetic field made to be induced in coil will operate on the conductive film of wafer. By changing a parameter (a frequency or an angle) influencing the skin effect of the conductive film and giving the parameter to coil, the state where a magnetic field is not made to penetrate relatively the film of wafer and the state where the magnetic field is made to penetrate relatively the film can be formed. From the variation of various values corresponding to the eddy current induced based on the change of state influenced by the skin effect of the conductive film, the film thickness of wafer can be measured with sufficient accuracy.