A disposable injector having a housing (10) in which are arranged at least one mechanical spring energy reservoir (50), at least one cylinder-piston unit (100) that can be filled at least in part with an active substance, at least one piston actuation plunger (60) and at least one trigger unit (80). The spring energy accumulator plunger (60) has at least one tension bar (61) with at least one support surface (63) at the upper end thereof. Locking elements (16) supported on the housing lie on the support surface(s) and are secured in the locking position by a triggering element (82) placed in a locking position (8). The triggering element has a release position (9) that causes the locking element (16) to be unlocked for release of the active substance.
