Based on the information of an object OB, a modifier volume MV for that object is set, the set modifier volume MV being then used to change an attribute. A gap region GR is then provided between the object OB and the modifier volume MV. The gap length GL of the gap region GR is changed depending on the distance H between the object OB and a projection plane PP (GL being increased as H increases). A modifier volume is drawn after a background and a plurality of model objects have been drawn. Thus, the shadow of a first model object is drawn to fall on a second model object while preventing the self-shadow of the first model object from falling on the first model object itself.