The housing 10 of the present invention having a proximal end 11 and a distal end (12); A hollow plunger rod (20) disposed within the housing; The housing and the dose as a concentric drum 40 is arranged to stretch between the plunger rod and the dose setting and dose two-way movement possible dose drum with respect to the housing and about at the time of delivery to the plunger rod (40); And to a drug delivery device comprising a plunger rod driving means for driving the hollow plunger rod towards the proximal end. The plunger rod driving means is a movably disposed within the hollow plunger rod is a hollow ratchet arm drum 30, which is fixedly connected to the elastic dose drum, the hollow plunger rod mutually releasably hollow ratchet arm drum which may be coupled to the 30; A dose activator (70) having a longitudinal bar 71 which is movably disposed within the hollow ratchet arm drum and a dose activator (70) which can be coupled releasably to one another is the longitudinal rods and hollow ratchet arm drum .; The dose and the dose setting knob fixed connection 100 that can be coupled releasably to the hollow drum ratchet arm to the activator; And a resilient element (110) for pressing in the direction of disengagement from the hollow ratchet arm drum combines the dose setting knob and the hollow ratchet arm drum the longitudinal bars of these dose activator is disposed between the hollow ratchet arm drum and the dose activator , the turning of the dose setting knob by a user during a dose setting and a resilient element 110 is forced to rotate with the hollow drum and the flexible ratchet arm dose drum.