Injection Device with a Sliding Scale

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 22 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.