A virtual endoscope image is generated based on an opacity template in which a pixel value of a three-dimensional image is associated with an opacity, the opacity template being capable of showing both of an inner wall of a large intestine region and an inner wall of a residue region present in the large intestine region on the virtual endoscope image, a viewpoint set in the vicinity of a boundary between a space region and the residue region in the large intestine region, a set surface set at a position separated by a previously set distance in a previously set line-of-sight direction from the viewpoint, and a pixel value on a light beam vector beyond the set surface among pixel values of the three-dimensional image on the light beam vector extending from the viewpoint.
