To detect the presence or absence of forgery in the punch hole area of a prepaid card.

A double refractive index film 16 having optical anisotropy is attached onto a substrate 11 in a punch hole area 14 and a reference face area 13 of a prepaid card 10. The optical anisotropy of the double refractive index film 16 can be detected when a linearly polarized light is transmitted through the double refractive index film 16, and the direction of polarization is changed. The card reader judges the presence or absence of card forgery by detecting whether or not a part without any prescribed double refractive index is present in the punch hole area 14 in the inserted prepaid card. A laser beam source, a pair of polarizers, and an optical sensor are used for the detection.