An automatic injection device for use with a syringe, including a housing element; at least one resilient element arranged to be located within the housing element; a needle guard slidably positionable with respect to the housing element; a control unit configured to be fixedly coupled with the housing element; a plunger rod biased axially forwardly under an urge of the at least one resilient element and configured to engage the control unit in a storage operative orientation, in which the plunger rod is prevented from forward axial displacement relative to the control unit under the urge of the at least one resilient element; and upon axial rearward displacement of the needle guard with respect to the housing element, the plunger rod is disengaged from the control unit and is permitted to be axially forwardly displaced relative to the control unit under the urge of the at least one resilient element.