A drug delivery apparatus (20) comprising a housing (22) extending between a distal end and a proximal end, and a syringe reel (90) that is rotatably fixed and axially movable within said housing Between a first position and a second position, a syringe loaded with a medicament (70) is held within said reel and includes a needle (72) having a proximal tip, said needle tip is disposed within said housing when said reel is in said first position, said needle tip projects from said housing beyond said proximal end for insertion into an injection site when said reel is in the second position, a plunger (130) extending axially from said end distal of the housing and can be moved manually in the proximal direction, said piston rotatably fixed and axially movable within said housing, means (98, 114, 134, 166, 168) in dic ho reel and said housing and said plunger to cause said reel to advance from said first position to said second position and to inject the medicament from said syringe when the piston is manually pushed proximally towards said housing, and means (106, 166) in said reel and said plunger to cause said reel to retract from the second position to a position in which said needle tip is again disposed within said housing when the plunger moves distally, characterized in that: a collar (170) is within said housing, said collar includes at least one cam surface (180)； means (160, 200) in said collar and said plunger for releasably locking said collar to said plunger so that it travels therewith during manual displacement of the plunger in the proximal direction that causes needle insertion and injection of the medicament of said syringe, said interlocking means are released when said collar is rotated from a first angular orientation within the housing to a second angular orientation within the housing； a pressure member (210) to force said collar and plunger away in an axial direction when said locking means is released to force said plunger distally into the hou
