The present invention provides an injection device including a syringe having a distal end for receiving a needle, and a plunger inserted into a proximal end. A guard is slidable on the syringe, has a proximal end, a distal end, and is biased from a first position wherein the needle is exposed toward a second position wherein the guard covers the needle. The syringe includes a body having a central cylindrical opening for receiving a medicine and the plunger, and further includes a pair of longitudinally extending members on opposite sides of the body. The injection device includes cooperating detents for retaining the guard and syringe in the first and second positions. A latch member is engageable by the plunger as the plunger is depressed to release the cooperating detents. Upon release, a spring element biases the guard toward the second position.