A decision part decides a representative edge direction using a predetermined angle range as a unit for each pixel area of a plurality of pixel areas of a photographic image photographed by a camera based on an edge angle of each pixel contained in the pixel area. An extractor extracts two of the pixel areas that are adjacent to each other as a pair area among the pixel areas of the photographic image, when the two pixel areas that are adjacent to each other have opposite representative edge directions. A determination part determines whether or not there is an attachable matter on a lens of the camera based on at least one of (1) a number of the pair areas extracted by the extractor and (2) a total sum of edge intensities of the pixel areas contained in the pair areas.