To provide a card authenticity deciding device capable of objectively and exactly deciding the authenticity of a card provided with a hologram image formed by a diffractive pattern on its surface.

The card authenticity deciding device is provided with a projection system 10 to project a laser measurement light flux Q1 to the hologram image 4 provided on the surface of the card 1 and formed by the diffractive pattern 3, a light reception system 20 having a Fourier transformation lens 21 to form the image of the diffractive pattern on a line sensor 22 by a diffractive reflection light flux Q2 reflected from the hologram image 4 and a deciding part 32 to decide the authenticity of the hologram image 4 based on a signal from the line sensor 22.