A medical injection device, including: a medication container having a mov-able piston； a push rod assembly displaceably disposed in the medical injection device, the push rod assembly having a plurality of spaced-apart position setting means disposed along the length thereof, the push rod assembly selectively displacing the movable piston to dispense medicament from the medication container； a spring to bias the push rod assembly to move toward the distal end of the medical injection device； a releasable restraining means configured to releasably restrain the push rod assembly in a locked state against the biasing of the spring, wherein, upon release of the releasable restraining means, the push rod assembly moves under force of the spring toward the distal end of the medical injection device； and an arming means configured to move the push rod assembly toward the proximal end of the medical injection device.
