Drug administration mechanism, method for using drug administration mechanism, and pump unit for drug administration mechanism

A dosing mechanism for dosing a patient with liquid medicine filled in a medicine vessel, comprising:

• a body;
• and a pump unit that is attached to the body,
• wherein the pump unit comprises:
• a pump in which a volume of a solution feeding part therein repeats expansion and shrinkage, thereby sucking the medicine from the medicine vessel and discharging the medicine to the patient;
• a suction-side pipe that extends from the pump toward the medicine vessel;
• a discharge-side pipe that extends from the pump toward the patient;
• a relief pipe whose one end is connected to the discharge-side pipe while the other end is located in a part whose pressure is lower than pressure inside the discharge-side pipe when the medicine is dosed;
• and
• a relief pipe on-off valve that opens and closes the relief pipe,
• wherein an excessive amount of the medicine staying in the discharge-side pipe passes through the relief pipe when a dosing route is closed and the relief pipe on-off valve is opened.