An identification device equipped with: a correct image generation unit, a degree-of-similarity calculation unit, and an authenticity determination unit. The correct image generation unit generates correct image data, which is compared with captured image data obtained by imaging a counterfeiting prevention medium for which an observed light pattern changes when the observation angle changes, said correct image data being generated in accordance with the observation angle, which is the angle formed by the imaging direction of the captured image data with respect to a reference line for the observed surface of the counterfeiting prevention medium. The degree-of-similarity calculation unit determines the degree of similarity between the captured image data and the correct image data. The authenticity determination unit performs an authentication determination to determine whether the counterfeiting prevention medium is appropriate, on the basis of whether the degree of similarity exceeds a preset threshold value.