A gas cylinder actuator with safety device for uncontrolled return of the piston-stem, comprising: a tubular containment jacket, two opposing heads for closing the tubular jacket, a first head which is provided with a through hole for passage and for translation guidance with respect to an axis of symmetry for a piston-stem, and a second, opposing head, a piston-stem, which comprises a stem portion and a piston portion, sealing elements which are arranged so as to act against the stem portion at the passage and guidance hole, a chamber for pressurized gas being defined between the tubular jacket, the heads and the piston-stem; such gas cylinder actuator comprises, between the first head and the piston portion, a bushing, which is coupled to the tubular jacket with elements of preventing translation with respect to the axis, and is designed to encounter the piston portion, the bushing being configured to at least be deformed in the event of impact with the piston portion owing to the uncontrolled return of the piston-stem, so as to allow the passage of the piston portion and the formation of a gas discharge passage between the piston-stem, the sealing elements and the passage and guidance hole.