PURPOSE: To display a polygon through a simple method by dividing the polygon beforehand into partial polygons by horizontal lines passing through its vertexes, and eliminating processing to change the ridgelines of the right and left at the time of the generation of display information.

CONSTITUTION: Each input value of the coordinate value and the luminance of each vertex in one or plural polygons is set in a polygon setting part 1, and in a polygon dividing part 2, on receiving these set values, a straight line parallel with a scanning line on a picture is drawn for every vertex of the polygon so as to pass through that vertex in order to divide the polygon into the plural partial polygons. Then, partial polygon information to show the positions and the luminances of the ridgelines of the right and left is obtained as information for displaying these partial polygons on the picture, and in a polygon display part 4, each partial polygon is displayed on the basis of the partial polygon information. Accordingly, at the time of the display of the polygon, the ridgeline need not be changed in any scanning line to display each partial polygon. Thus, the polygon can be displayed through the simple method.