The present invention allows a high-speed printing by a print head in which nozzles are arranged with a high density to reduce eddy flow caused between the print head and a print medium, providing an image with a high quality. Thus, the present invention allows the same printing region of the print medium to be sequentially printed by the respective nozzle arrays provided in the print head in accordance with image data thinned-out by the mask pattern M, thereby completing the image by multi-pass. Then, a plurality of pieces of image printed to be printed to the same printing region at which the nozzle arrays pass in one pass are alternately thinned-out by different high and low thinning-out ratios in the direction in which the nozzles are arranged.