1. A person recognizing apparatus comprising: a biometric information inpu unit to input biometric information of persons subject to recognition; a registered information memory to store biometric information of persons subject to recognition in advance as registered information; a recognizer to obtain similarities of biometric information input by the biometric information input unit and registered information stored in the registered information memory by collating both of them and recognize the person based on the obtained similarity; and a registered information updating unit to judge whether the similarity obtained by the recognizer is within a prescribed updating range and based on being judged as the similarity is within the prescribed updating range, update the registered information stored in the registered information memory by using the biometric information input by the biometric information input unit.