An apparatus and method are provided to enable high speed printing of an image with high resolution while suppressing degradation of image quality due to white stripes and density variations. In an ink jet printing apparatus using a multi-pass printing system, the same scan print area is divided at a predetermined pitch and the printing duties of the divided areas determined by the thinning out mask pattern are set to different values. In regard to the same scan print area formed by a plurality of the main scans, the divided areas corresponding to the ends of the print head have their printing duties set smaller than those of the divided areas on the inner side of the ends of the print head.