The invention refers to an injection device (1) for automatic spring driven injection of a liquid drug by which doses of an individual size can be set by a user, the injection device (1) comprising: a housing (3) defining an interior space and having a longitudinal window (7), a rotatable dose dial (2) axially retained in relation to the housing (3), a rotatable scale drum (4) carrying indicia (6) for indicating the size of the set dose, wherein the scale drum (4) is functionally coupled to the dose dial (2) to rotate when the dose dial (2) is rotated to set a dose, a sliding element (11) provided with a sliding window (12), which sliding element (11) is adapted to slide axially in relation to the housing (3) during dose setting, and through which sliding window (12) the indicia (6) carried by the scale drum (4) is visible such that the longitudinal window (7) and the sliding window (12) in combination with the indicia (6) form a dose size display, and wherein the scale drum (4) rotates within the interior space defined by the housing (3) during dose setting and wherein the inner surface of the sliding element (11) is provided with an internal feature (29) engaging an external thread (5) provided on the outer surface of the scale drum (4) and wherein the sliding element (11) is further axially guided in the housing (3) such that the sliding element (11) moves axially when the scale drum (4) is rotated, wherein a drive spring (14) is attached to the scale drum (4) with one end and to the housing (3) with another end such that relative rotation between the scale drum (4) and the housing (3) charges the drive spring.La présente invention concerne un dispositif dinjection (1) pour injection entraînée par ressort automatique dun médicament liquide au moyen duquel des doses dune taille individuelle peuvent être définies par lutilisateur, le dispositif dinjection (1) comprenant : un boîtier (3) définissant un espace intérieur et ayant une fenêtre longitudinale (7), un cadr
