A liquid injector comprising a liquid injection head mounted on a carriage and reciprocated widthwise of a target, and valve unit mounted on the carriage to receive a supply of liquid through a feed passageway from a liquid receiving body and to feed the liquid to the liquid injection head. The valve unit comprises a pressure chamber connected to the liquid receiving body through the feed passageway, a valve adapted to open or close the feed passageway to feed the liquid to the pressure chamber, and a flexible film member adapted to be displaced on the basis of a negative pressure produced concomitantly with a decrease in the amount of liquid in the pressure chamber, so as to actuate the valve.
