The present invention relates to a device for expelling a predetermined quantity of medicament comprising driving means comprising an energy-accumulating member, a nut, and a driver for driving a pressure means and activation means for activating said driving means wherein said pressure means comprises a movable wall part arranged inside a 2 container and a threaded plunger rod arranged to interact with said driving means for pushing said movable wall part forwardly, and wherein said activation means comprises a manually operated push button arranged on the front end of the device for promoting an ergonomic handling of the device and wherein said activation means are capable of interacting with said driving means in a stepwise mode such that each time said push button is depressed said pressure means moves an step exerting pressure on the medicament inside the container and expelling a predetermined quantity of the medicament through the opening.
