Disclosed is an inkjet printing apparatus for forming an image by repeatedly causing the scanning of a printhead that prints an image in a scan area using inks of a plurality of types. Residual duty, which is obtained by quantifying the mixed state of the inks used in printing the image in the scan area, is defined. The residual duty with regard to the next scan area is found from image data, the scanning direction for printing in the next scan area is decided based upon the residual duty, and the area is printed in the scanning direction that has been decided. Thus, back-and-forth scanning and unidirectional scanning are used jointly in appropriate fashion in accordance with the printed image. As a result, high-quality printing of an image becomes possible and a higher printing speed is achieved.