An ocular fundus image is captured by a fundus camera. Blood vessel regions are erased from the ocular fundus image, and a luminance region greater than a prescribed luminance threshold value and having an area equivalent to a predetermined standard disc area is extracted as a region having a standard disc area. The region having the standard disc area is divided into a plurality of regions by a plurality of dividing lines extending radially from the center of gravity thereof, and divided regions are scanned radially from the center of gravity while angles are shifted to detect in each individual region a point at which luminance variation reaches a maximum. The contour line of the disc region is derived from these points.
