Abstract: An injection device for injecting set doses from an ampoule (2) mounted in the device, which doses are set by operation of a dose setting button (7) by which operation elastic torsion rods (14) positioned parallel with the longitudinal axis of the device are twisted. By the dose setting a torque is transmitted from the dose setting button (7) to the rods (14) through gear transmissions comprising a toothing (11) carried by a tubular (8) part coupled to the dose setting button (7) to rotate with this button. The toothing (11) engages pinions (13) fixed to the proximal ends of the torsion rods (14), which are made from a super elastic material, which can stand a deformation larger than 2% without being permanently deformed.