PURPOSE: To prevent the clogging of the first orifice of the ink-drop injector mainly resulting from drying and the adhesion of dust, and to obtain desired injection at all times by coating the first orifice with ink in a front chamber when printing is not conducted.

CONSTITUTION: After printing operation is completed, the ink-drop injector 1 is returned to a home position HP, the second orifice 10 is covered with a cover body 20, the front chamber 8 is interrupted from the outside, a valve gear 17 is changed over and communicated with atmospheric air, and the chamber is interrupted from an air pump 14. When the pump 14 is driven at that time, an ink tank 11 is pressurized by an air current 16, the pressure of an ink chamber 5 in the vicinity of the first orifice 7 rises slowly more than the front chamber 8, and the outflow of ink is assisted by applying electric signals to a piezo-electric diaphragm 2. The first orifice 7 is coated with ink, is brought to a positive supply condition without causing clogging due to drying, etc. and does not suck bubbles by the outflow.