A kind of injection device, comprising: shell has proximally and distally Medicament storage portion Backstop is used to for drug being discharged from the medicament storage portion Cavity with inflatable volume, the cavity are arranged to when the cavity is at least partially filled with fluid, move the storage unit or the backstop along distal direction And fluid storage section, it is configured to distribute a fluid in the cavity Wherein the cavity includes flexible pipe, and the fluid storage section is configured to distribute a fluid in the flexible pipe.
