Activation assembly for an automatic injection device that includes a deflected element and a housing, where the deflected element can be released by operating the activation assembly for movement in a first axial direction relative to the housing, where the activation assembly comprises : a button to be pressed by a user, where said button is movable in the first axial direction in relation to the housing from a first axial position to a second axial position, where said button includes a retention element that includes a retention surface and a recessed surface, wherein said recessed surface is separated at a distance in a first angular direction from said retention surface； a first coupling surface arranged in the deflected element and movable therewith； a locking element supported within said housing so that it can rotate therein, wherein said blocking element includes a button coupling element； a second coupling surface disposed in said locking element for coupling with said first coupling surface, wherein said coupling surface of said first and second surface limits the movement of the deflected element in the first axial direction； wherein at least one of said first and second coupling surface is ramp-shaped for a cam guiding effect between said first and second coupling surface； said retention element, when said button is arranged in said first axial position, has said retention surface in a relationship in contact with said coupling element to the button to prevent rotation of said locking element in said first angular direction, wherein said rotation prevention keeps said second coupling surface in engagement with said first coupling surface； and wherein said retention element, when said button is disposed in said second axial position, has said free retention surface of said coupling element to the button to allow said locking element, under the influence of the cam-guided effect of said first and second coupling surface, as the deflected element is defle
