1. A computer readable storage medium ( 11 e ) having stored thereon an image processing program for drawing an image of a curved surface as viewed from a virtual camera situated in a virtual three-dimensional space, an undulation of the curved surface being defined by a distance from a virtual plane surface arranged in the virtual three-dimensional space, the image processing program causing a computer to execute: a plane surface division step of dividing the virtual plane surface into a plurality of polygonal shape regions such that the closer a region is to the virtual camera, the smaller areas the region is divided into; a first distance reading step of reading, from storage means, distance information indicative of distance from the virtual plane surface, with respect to respective vertices of the plurality of polygonal shape regions; a first coordinate point calculation step of calculating coordinate points of position which are respectively distanced from the vertices composing the plurality of polygonal shape regions by distances indicated by the distance information, which is read in the first distance reading step, in a direction perpendicular to the virtual plane surface; a polygon generation step of generating polygons by using the coordinate points calculated in the first coordinate point calculation step as polygon vertices which define the polygons, the number of the polygons being substantially constant in each of the plurality of the polygonal shape regions; and a drawing step of drawing an image of the polygons which are generated in the polygon generation step, the image as being viewed from the virtual camera.