Multilayer polygon data for constructing multilayer polygonal models and a height map including height data values, arranged in a two-dimensional array, each of which indicates the height of each position provided on a three-dimensional object to be drawn, are read from a storage device. Then, the height of a layer of the multilayer polygonal models is compared to the height data value of a position provided on the height map, so as to determine a visible region provided on the layer of the multilayer polygonal models. And then, the visible region which is determined as described above and provided on the layer of the multilayer polygonal models is drawn in a predetermined color. Thus, it is possible to easily draw, in three-dimensional image processing, a three-dimensional object, such as an accumulation of snow, soil, sand, or bricks, positioned in the virtual space, regardless of the shape of the object.