A biometric authentication device, comprising: a first biometric sensor that is arranged to obtain a biometric image of a biometric modality of a user; a second biometric sensor that is arranged to obtain a biometric image of the same biometric modality of the user and has a device structure to achieve lower image quality than the first biometric sensor; an authentication process unit that is arranged to perform an authentication by determining whether a similarity between authentication features extracted from the biometric images obtained by the first biometric sensor with enrolled templates of an enrollment database is equal to or more than a first threshold (TH 0); and a process unit arranged to lower image quality of the biometric image obtained by the first biometric sensor in a case where the similarity between the authentication features extracted from the biometric image obtained by the first biometric sensor and any of the enrolled templates is equal to or more than the first threshold (TH 0), wherein, when a similarity between the authentication feature extracted from the biometric image obtained by the second biometric sensor and the enrolled templates is equal to or greater than a second threshold (TH 1), the authentication process unit authenticates the user, and, when a similarity between the authentication feature extracted from the biometric image obtained by the second biometric sensor and the enrolled templates is less than the second threshold (TH 1) and equal to or greater than a third threshold (TH 2), the second threshold (TH 1) being greater than the third threshold (TH 2), the authentication process unit authenticates the user if a similarity between an authentication feature extracted from the biometric image of which the image quality is lowered by the process unit and the authentication feature extracted from the biometric image obtained by the second biometric sensor is equal to or more than a fourth threshold (TH 3). a first biometric sensor that is arranged to obtain a biometric image of a biometric modality of a user; a second biometric sensor that is arranged to obtain a biometric image of the same biometric modality of the user and has a device structure to achieve lower image quality than the first biometric sensor; an authentication process unit that is arranged to perform an authentication by determining whether a similarity between authentication features extracted from the biometric images obtained by the first biometric sensor with enrolled templates of an enrollment database is equal to or more than a first threshold (TH 0); and a process unit arranged to lower image quality of the biometric image obtained by the first biometric sensor in a case where the similarity between the authentication features extracted from the biometric image obtained by the first biometric sensor and any of the enrolled templates is equal to or more than the first threshold (TH 0), wherein, when a similarity between the authentication feature extracted from the biometric image obtained by the second biometric sensor and the enrolled templates is equal to or greater than a second threshold (TH 1), the authentication process unit authenticates the user, and, when a similarity between the authentication feature extracted from the biometric image obtained by the second biometric sensor and the enrolled templates is less than the second threshold (TH 1) and equal to or greater than a third threshold (TH 2), the second threshold (TH 1) being greater than the third threshold (TH 2), the authentication process unit authenticates the user if a similarity between an authentication feature extracted from the biometric image of which the image quality is lowered by the process unit and the authentication feature extracted from the biometric image obtained by the second biometric sensor is equal to or more than a fourth threshold (TH 3).