A serial type inkjet printing apparatus performs the following processing. A slant is set between the nozzle arrayed direction and the carriage moving direction for each printing column in the carriage moving direction. The carriage position is detected. Image data stored in a print buffer in association with each printing column is divided based on the detected carriage position and the slant in the printing column corresponding to the set position of the carriage. The image data is read by separating it into respective data used for first-and-second-scan printings by the printhead in an identical region, based on the detected carriage position, and the slant in the printing column corresponding to the set position of the carriage. Printing is performed by first-and-second-scanning the printhead on the identical region, using the read image data.