The invention provides a medicine ejection device which provides stable ejection even when a reservoir with high sealability is used and can eject an appropriate amount of medicine. A medicine ejection portion 1 includes an ejection nozzle 1a for ejecting a medicine and an element 1b which generates energy for ejecting the medicine from the ejection nozzle 1a, and is connected to a medicine storing portion 2 for storing the medicine. The medicine storing portion 2 is blocked from the outside air except a path through the ejection nozzle 1a, so that when the medicine is ejected from the ejection nozzle 1a, a pressure difference is formed between the outside and the inside of the medicine storing portion 2. A pressure unit 3 which is a feature of the present invention pressurizes a movable wall 5 when ejecting a medicine, which is displaced so that the volumetric capacity of the medicine storing portion 2 decreases due to the pressure difference.
