An autoinjector having a body (1, 2), a reservoir (S) including a piston, a piston rod (5) movable between a rest position and an injection position, an actuator spring (6) urging the piston rod (5) towards the injection position, and a force-adjustment system (7, 8) to exert a force (F2) on the piston rod (5), adding to the force exerted by the spring (6) at the beginning of injection. The system has two pivot members (7) co-operating with the piston rod (5), the pivot members (7) connected together by two resilient elements (8). The body (1, 2) includes a sleeve (3), the pivot members (7) pivotally mounted on the sleeve (3) to pivot about stationary pins (79). The autoinjector includes an end-of-injection indicator that includes an indication portion movable and/or deformable relative to the body (1, 2) to co-operate with a viewing window after the end of injection.