1. An image display device for direct drawing apparatus for performing direct drawing of a predetermined pattern on a drawing object by scanning with a drawing beam, comprising: an acquisition part for acquiring design data in a vector format describing said pattern; a specified drawing raster image processing (RIP) parameter setting part for setting a specified drawing RIP parameter to be used for drawing RIP development of said design data; a processing area setting part for setting a display object portion of said design data to be subjected to said drawing RIP development as a processing area; a display RIP development part for performing display RIP development of a portion of said design data, which corresponds to said processing area, by using said specified drawing RIP parameter, to thereby obtain a specified image; and a display part for visibly displaying said specified image, wherein: said display RIP development performed by said display RIP development part is a RIP development in which the amount of processed data is smaller than that in said drawing RIP development for said direct drawing, said display RIP development part performs RIP development of said portion corresponding to said processing area by using said specified parameter, to thereby obtain said specified image and also performs RIP development of said portion corresponding to said processing area by using a predetermined reference parameter, to thereby obtain a reference image, and a display part visibly displays said specified image and said reference image, overlapping each other and displays a difference between said specified image and said reference image, being visually distinguished from a common portion between said specified image and said reference image.