To eliminate influence of cross-talk in an on-demand multi-nozzle ink jet head, drive pulses to be applied to piezoelectric elements for driving nozzles aligned in a row are individually adjusted so that the nozzles eject ink droplets at the same speed when the nozzles are driven simultaneously. To the piezoelectric elements which are deactuated during printing, a dummy drive pulse having a voltage level in a range from 50 to 75% of a minimum voltage for ejecting an ink droplet is applied, whereby the ejection speed achieved when individual nozzles are driven approaches the ejection speed achieved when all nozzles are driven simultaneously. As such, the print quality is improved.