1. A face authentication system comprising: a photographing unit for detecting a face image of an authentication target person by using an auto focus lens equipped therewith; a distance extraction unit for extracting a distance from the photographing unit to a face of the authentication target person; a feature extraction unit for extracting feature points and distances therebetween of the face image for the authentication target person, which are detected by the photographing unit; an analysis unit for performing an analysis by comparing a distance to the face of the authentication target person extracted from the distance extraction unit with pre-registered distance information to the face of the authentication target person, and comparing feature points and distances therebetween of the face image for the authentication target person, which are extracted from the feature extraction unit, with pre-registered information of the face image of the authentication target person; and an authentication unit for authenticating the authentication target person according to an analysis result obtained by comparison of the analysis unit.