The challenge of the present invention is to prevent a crook line part of a dotted line from being displayed in half tone. The present invention is contrived to calculate a center coordinate of a texture pixel in a zone including a reference texture beginning point coordinate S_Begin as reference texture corrected beginning point coordinate S_Begin′. It is followed by calculating a center coordinate of a texture pixel in a zone including a reference texture end coordinate S_End as reference texture corrected end coordinate S_End′. A crook line part of a dotted line is drawn by fixing a reference coordinate to the S_Begin′ or S_End′ if a pixel to be drawn exists within a fixing section.