A disposable injector with a housing (10) in which are arranged at least one mechanical spring energy store (50), at least one cylinder-piston unit that can be filled at least temporarily with an active substance, at least one piston actuation plunger (60) and at least one triggering unit (80). The spring energy store comprises at least one pre-loaded spring element. The spring-loaded piston actuation plunger has at least one traction rod (61) which can be moved transversely, at least in certain regions, and by means of a supporting portion supports the tensioned spring energy store on at least one resting surface (37) of the housing. An actuatable triggering slide device (82) unlocks the disposable injector and releases the supporting portion to allow it to move away from the resting surface.