Ink-jet heads having respective sets of ink ejection nozzles arranged longitudinally at a predetermined pitch are arranged in the moving direction of a sheet of art paper with a predetermined distance separating them from each other. The pitch Q separating the ink ejection nozzle of one of the ink-jet heads located at an end thereof from the corresponding ink ejection nozzle of the other ink-jet head located at the proximal end of the former ink ejection nozzle is made smaller the predetermined pitch P of arrangement of the ink ejection heads of the ink-jet heads.