According to the present invention, each printing head includes chips wherein a plurality of nozzles are prepared. The density of dots formed by ejecting ink from the nozzles is detected for each chip, and when a density difference between the chips is smaller than a predetermined value, print data are corrected, and the number of dots is adjusted so as to reduce the density difference. When the density difference is equal to or greater than the predetermined value, first, a drive pulse for the nozzles is modulated and the volume of ink to be ejected for one dot is adjusted so as to reduce the density difference. Thereafter, the print data is corrected, and the number of dots to be formed is controlled so as to reduce the density difference.