In displaying overlapped images on a monitor, a rendering display device is provided for the purpose of easily overlapping images without having complicated mask data or the like. In the rendering display device, when at least one of image data stored in non-display memories is updated and if there exists an image whose layout information specifies that its image is displayed in the foreground of images corresponding to the updated image data, the updated image data and the image data specified to be displayed in the foreground are transferred to an entire-image non-display memory.
