A pressurized injection device comprises a mechanical loading mechanism comprising a double set of rackets (17,18) and ball bearings/pins running in a curved track (20) which enables a resilient element (7) to be pre-stressed by—twisting the two outer house parts of the device relative to each other back and forth. When twisted in one direction one set of rackets (17) engages the teeth of the piston rod (9) connected to the resilient element and when twisted in the opposite direction, the other set of rackets (18) engages same piston rod. The resilient element is set off to engage a plunger of a container holding a drug to be injected by pressing the release button (1), which can be secured by a safety switch.