An obtainment unit (311) obtains characteristics information of a biometric image captured while casting first or second illumination light onto an authentication target. The first illumination light includes light of a first wavelength, and the second illumination light includes light of the first wavelength and light of a second wavelength. A reading unit (312) reads characteristics information of a biometric image captured while casting illumination light cast onto the authentication target from a storage unit that stores first characteristics information of a first biometric image and second characteristics information of a second biometric image. The first biometric image is captured while casting the first illumination light onto a registration target, and the second biometric image is captured while casting the second illumination light onto the registration target. A calculation unit (313) calculates a similarity between the obtained characteristics information and the characteristics information read from the storage unit, and an authentication unit (314) conducts authentication.