A face authentication apparatus includes a high tone image acquiring section, a tone converting section, a face characteristic extracting section and a face collation section. The high tone image acquiring section acquires a high tone image containing the face of a walker. The tone converting section converts the acquired high tone image to a low tone image by tone conversion processing which optimizes the brightness of a face area in the high tone image acquired by the high tone image acquiring section. The face characteristic extracting section executes an extraction processing for the face characteristic information based on the low tone image whose brightness is optimized by the tone converting section. Further, the face collation section executes face collation processing based on the low tone image whose brightness is optimized by the tone converting section.