Backflow prevention structure and a backflow prevention unit for a liquid medicine injection device

摘要

A backflow prevention structure, which is to be connected to a liquid medicine inlet of a liquid medicine injection device for injecting a liquid medicine in a liquid medicine retaining vessel of the liquid medicine injection device into a body part, includes a backflow prevention valve element provided at the liquid medicine inlet for preventing backflow of the liquid medicine from the liquid medicine retaining vessel. The backflow prevention valve element has a beaklike nonreturn valve and an annular valve and the liquid medicine is introduced into the liquid medicine retaining vessel through the beaklike nonreturn valve, and the liquid medicine in the liquid medicine retaining vessel is allowed to flow in a reverse direction via the annular valve when a negative pressure is produced on one side of the backflow prevention valve element opposite to the liquid medicine retaining vessel.