Abstract: A drug ejection apparatus comprises a drug ejection assembly having an ejection port and an element for generating energy for ejecting a drug through the ejection port, a drug container connected with the drug ejection assembly for holding the drug, a pressure sensor unit for sensing a pressure change in the inside of the drug container in correspondence with ejection of the drug through the drug ejection assembly, and a drive control unit for deciding driving conditions of the element for ejecting a prescribed amount of the drug by reference to an output level of the pressure sensor unit on driving the element under prescribed conditions.