Abstract: An on-demand type ink jet printing apparatus which prints out data in various forms such as characters and numerals by the combination of dots formed by ink droplets on a sheet of paper. An ink ejection head of the printer includes control electrodes disposed in at least one ink passageway. Ink droplets are formed and caused to fly by electric fields developed in the vicinity of the control electrodes when voltages are applied thereacross. Multiport ink ejection is achieved by the provision of a plurality of ink passageways in the head. The voltage supply to the control electrodes is controllable so that ink droplets may be formed and caused into flight in response to print signals.A channel defining each ink passageway can be shaped easily yet with accuracy utilizing an etching characteristic particular to a specific crystal face.A plurality of acceleration electrodes may be employed to promote desirable flight of ink droplets.