A sensor unit (30) including a coil is disposed on the lower surface of a conveyance path (20) for a coin (10), whereby a magnetic field larger than the maximum diameter of the coin (10) is generated, and a parallel resonance impedance is calculated by means of frequency sweeping. An inductance is calculated from the resonance frequency of the parallel resonance impedance, and a resistance component at the parallel resonance impedance is calculated from the impedance value and the inductance value. The denomination and authenticity of the coin (10) are identified by using a variation in the inductance as an index for discriminating the size of the coin (10), and a variation in the resistance as an index for discriminating the material of the coin (10).
