The present invention relates to an injection device for automatic spring driven injection of a liquid drug. The injection device has a dose setting mechanism by which doses of an individual size can be set by a user, and a mechanical dose size display for displaying the size of the set dose. A housing (2) defines an interior space and has a longitudinal window (3) through which a rotatable scale drum (20) can be viewed. The scale drum (20) is coupled to a rotatable dose dial button (10) which is axially retained in relation to the housing (2) and by which the individual doses can be set. The injection device further comprises a sliding element (30) provided with a sliding window (35) and which sliding element (30) is adapted to slide axially in relation to the housing (2) during dose setting, and through which sliding window (35) indicia (22) carried by the scale drum (20) is visible such that the longitudinal window (3) and the sliding window (35) in combination with the indicia (22) form the dose size display. The rotatable scale drum (20) rotates within the interior space defined by the housing (2) during dose setting and the sliding element (30) is coupled to the scale drum (20) such that the sliding element (30) move axially within the boundaries of the housing (2) when the scale drum (20) is rotated.La présente invention concerne un dispositif dinjection pour une injection actionnée par ressort automatique dun médicament liquide. Le dispositif dinjection possède un mécanisme dajustement de doses avec lequel des doses individuelles peuvent être ajustées par un utilisateur, et un dispositif mécanique daffichage de la quantité constituant la dose pour afficher la quantité constituant la dose ajustée. Un boîtier (2) délimite un espace intérieur et possède une fenêtre longitudinale (3) à travers laquelle un tambour gradué rotatif (20) peut être observé. Le tambour gradué (20) est couplé à un bouton de composition de dose rotatif (10) qui est retenu axialement par
