Printing on an area of a printing medium in which printing locations may be significantly deviated due to inaccurate feeding of the printing medium can be performed, without degrading image quality. Specifically, when lines in this area (second area) are printed using four scanning operations (passes) of a print head, a duty in masking process is set at zero for the scanning operation (pass A) after a change-line operation for feeding the printing medium with a possible large shift feeding error, and is distributed to other scanning operations. Thus, no dots are formed during this scanning operation (pass A), thereby preventing significantly deviated dots from being formed.