Frequency dependency of an electrostatic actuator is improved by setting a driving voltage waveform. It has an electrode (11) that counters a vibrating plate (21) that constitutes a part of the surface of a wall of an ink chamber, and the vibrating plate (21) and the electrode are provided with a predetermined gap (40). Pulse voltage is applied between the electrode (11) and the vibrating plate (21), displacement of which is carried out by electrostatic force that pressurizes ink in the ink chamber according to mechanical resilience of the vibrating plate (21) such that an ink drop is ejected. The vibrating plate (21) is vibrated such that it may contact the electrode (11), ejecting the ink by one or a plurality of electric pulses. A ratio of the period during which the vibrating plate contacts the electrode to the period required to form a pixel is regulated to be equal to or less than (200−2.79×PV) %, where PV is a per cent ratio of displacement volume of the vibrating plate to a vibrating chamber that is the space defined by the vibrating plate and a board of the electrode.