rack 10 which is unmovable relative to the gear box provides a gearing ratio of 2 1 for the longitudinal movement relative to the syringe housing 1 for the movable rack 15 and the connector 12 which carries the shaft 11 of the gear wheel fig3 and 4 shows a preferred embodiment wherein only one size gear wheel is used and wherein elements corresponding to elements in fig1 and 2 are given the same references as these elements with a prefixed u201c 1 u201d for manufacturing reasons minor changes are made so the partitioning wall 102 and the tubular element 105 are made as two parts which are by the assembling of the device connected to each other to make the assembled parts act as one integral part the same way the dose setting drum 117 and the dose setting button 118 are made as two parts which are fixed firmly together a circumferential recess 107 is provided as an outer recess at the free end of the tubular part 105 and a ring shaped coupling element is provided as an inner bead 108 on the gear box element 109 which bead engages the recess 107 to provide a rotatable but not axially displaceable connection between the tubular part 105 and the gearbox a tubular element 120 having ridges 122 which engages recesses 123 on the gearbox is at its upper end closed by a button 119 from which a force provided by pressing this button is transmitted to the tubular element 120 the gearbox is formed by two shells which together form a cylinder fitting into the tubular element where the shells are guided by the engagement between the ridges 122 and the recesses 123 racks 110 and 115 are.