Three discharge port groups, each having a plurality of discharge ports, discharge inks of three primary colors to record swaths of the respective colors on a recording medium and repeat the discharging to complete a record. Joints of each of Y, M and C color swaths are spaced from joints of swaths of the other two colors by an equal distance, and the discharge port groups are offset from each other by 8n times of a discharge port pitch in a direction of feed of the recording medium. In a number of image buffers corresponding to the discharge ports, image data in one buffer is separated from image data in a different image buffer by an amount that is an integer multiply of one 8 bit byte.