A plunging apparatus (1) for a syringe. The plunging apparatus is installed in a threaded driving mechanism of an injection device and can be connected to a drug barrel (2). A push element (10) of the plunging apparatus (1) is combined with a one-way check valve element (20) and then assembled in an engagement element (30). A rear end of the engagement element (30) is connected to a pushing rod (40). A front end of the pushing rod (40) is internally provided with an ejection element (50) and a spring (60). A threaded ring (70) is connected to the outside of the pushing rod (40) in a threaded manner. An injection pushing rod (80) is loaded inside the pushing rod (40). The engagement element (30) of the plunging apparatus (1) is loaded into a rear end opening (2B) of a drug barrel (2), such that a snap fastener (32) of the engagement element (30) is pressed against a hook (52) of the ejection element (50) at the periphery of the rear end opening (2B) of the drug barrel (2), and causes the pushing apparatus (1) to be in an unlocked state. The spring (60) drives the ejection element (50) to eject forwards and the ejection element (50) pushes the push element (10) forwards until the same abuts a plunger (2A) in the drug barrel (2), such that the drug barrel (2) is combined with the injection device and immediately ready to use. The present invention eliminates the need for a user to manually close the space by pushing a push element (10) of an injection device forward until the same abuts a plunger (2A) inside the drug barrel (2), thereby improving the convenience of using an injection device.L'invention concerne un appareil plongeur (1) pour seringue. L'appareil plongeur est installé dans un mécanisme d'entraînement fileté d'un dispositif d'injection et peut être relié à un cylindre de médicament (2). Un élément de poussée (10) de l'appareil plongeur (1) est combiné avec un élément de clapet anti-retour unidirectionnel (20) puis assemblé dans un élément de mise en prise
