The present invention, possible condensation in the tubular casing 12, the tubular chassis (2); Case 12 as the tubular carrier (7) slidably disposed about the chassis 2 from the inside, a carrier one to contain a syringe (3) with a hollow injection needle (4) (7), the drive spring (8) and a carrier sub-assembly comprising a plunger (9) to transfer the load of the drive spring (8) on the stopper (6) of the syringe (3), wherein the syringe (3) is a co-axial dislocation between the carrier (7) possible to lock the carrier sub-assembly; Case the trigger button 13 arranged in a side or a circle over anthropogenic or case 12 in 12; A carrier spring disposed around the control (7) (19); The proximal end of the control spring 19, the carrier 7 and the chassis (2), the carrier (7) in order to advance the distal end of the control spring 19 for the needle extending along the relative axial position of the, or needle needle extending control mechanism for connecting to a chassis (2) for the retraction (24); Carrier 7 is a time at least substantially reaches the proximal position hayeoteul extended, the plunger release mechanism 27 arranged to release the plunger (9) for scanning; With a detent mechanism 18 is disposed for connecting the chassis (2) to the carrier (7) for co-axial electric potential to the case 12, at this time, the chassis from the trigger button 13 is operated the carrier 7 (2) is arranged to remove the needle extension control mechanism 24 to switch to the carrier 7, the proximal end to the needle extension of the control spring 19, to move the carrier (7) to the chassis (2) detent mechanism (18) to allow; The distal end of the control spring 19, to the carrier (7) to the needle retracted, or otherwise, comprising a syringe retraction control mechanism (25) arranged to couple the casing 12, the liquid drug ( It relates to an automatic injector (1) for dispensing a single serving M).