1. An authentication apparatus for authenticating a person by determining whether input data belongs to a biologic object in accordance with a predefined condition based on biometric data of a genuine person and whether the input data matches with registered biometric data of the genuine person, said authentication apparatus comprising: a forgery data extractor configured to extract forgery data from the input data, said forgery data being for determining whether the input data belongs to a biologic object or a fake; a forgery similarity calculator configured to calculate forgery similarity of biometric data of the genuine person, said forgery similarity indicating similarity to a fake; a forgery difficulty calculator configured to calculate forgery difficulty of biometric data of the genuine person, said forgery difficulty indicating difficulty of forgery; a determination threshold setter configured to determine a forgery determination threshold on the basis of the forgery similarity and the forgery difficulty; a forgery score calculator configured to calculate a forgery score of the input data on the basis of extracted forgery data, said forgery score indicating likelihood of forgery; and a forgery determiner configured to determine whether the input data belongs to a biologic object by comparing calculated forgery score with the forgery determination threshold.