A blind spot estimation portion for estimating the blind spot region of the object in the bucket; a blind spot region shape estimation portion for estimating a shape of the object in the blind spot region; and a volume estimation portion for estimating a volume of the object in the blind spot region are included, the blind spot estimation portion estimates the blind spot region by mesh disparity data obtained from a captured image of the object in the bucket imaged by a plurality of cameras, the blind spot region shape estimation portion estimates the shape of the object in the blind spot region by the mesh disparity data, and the volume estimation portion estimates the volume of the object in the blind spot region based on the shape of the object in the blind spot region estimated by the blind spot region shape estimation portion and a shape of a bottom of the bucket.