An injection device comprising a pre-filled syringe and a safety device for the pre-filled syringe, wherein the safety device comprises - an adaptor means, - a hollow support body (3.1) the injection device characterised by: - a hollow outer body (3.2), substantially receiving the support body (3.1) within and slidably arranged with respect to the support body (3.1), wherein a proximal surface of the outer body (3.2) is arranged to abut a piston rod (2.4) connected to a piston (2.6) of the pre-filled syringe, so that the piston rod (2.4) and the piston (2.6) may be moved by manually pushing the outer body (3.2) in a distal direction to perform an injection stroke, whereby a medication or drug contained in an inner cavity (2.1.2) of the pre-filled syringe is expelled through a hypodermic needle (2.3), wherein the adaptor means is adapted to affix the pre-filled syringe thereto, whereby the adaptor means engages a barrel (2.1) of the pre-filled syringe and wherein the adaptor means comprises at least one locking projection (1.1.1) that is adapted to lock the adaptor means to the support body (3.1), wherein the adaptor means is retained within the support body (3.1) in a manner that the adaptor means is movable with respect to the support body (3.1) by a proximal movement of the outer body (3.2) with respect to the support body (3.1) from a first position, in which a hypodermic needle (2.3) of the pre-filled syringe projects distally from the support body (3.1), to a second position, in which the hypodermic needle (2.3) is surrounded by the support body (3.1), wherein the locking projection (1.1.1) of the adaptor means engages a locking recess (3.1.3) formed into the support body (3.1) to irreversibly lock the adaptor means in the second position, wherein a radial projection (3.2.1.1) of the outer body (3.2) protrudes radially inwards through a longitudinal slot (3.1.1) formed in the support body (3.1), wherein the radial projection (3.2.1.1) moves along the longitudinal slot (3.1.1) when the outer body (3.2) is moved during the injection stroke such that at the end of the injection stroke, the radial projection (3.2.1.1) catches a distal collar (1.1) of the adaptor means to couple the adaptor means to the outer body (3.2) such that proximal movement of the outer body (3.2) with respect to the support body (3.1) can move the adaptor means from the first position to the second position. - an adaptor means, - a hollow support body (3.1) the injection device characterised by: - a hollow outer body (3.2), substantially receiving the support body (3.1) within and slidably arranged with respect to the support body (3.1), wherein a proximal surface of the outer body (3.2) is arranged to abut a piston rod (2.4) connected to a piston (2.6) of the pre-filled syringe, so that the piston rod (2.4) and the piston (2.6) may be moved by manually pushing the outer body (3.2) in a distal direction to perform an injection stroke, whereby a medication or drug contained in an inner cavity (2.1.2) of the pre-filled syringe is expelled through a hypodermic needle (2.3), - a hollow outer body (3.2), substantially receiving the support body (3.1) within and slidably arranged with respect to the support body (3.1), wherein a proximal surface of the outer body (3.2) is arranged to abut a piston rod (2.4) connected to a piston (2.6) of the pre-filled syringe, so that the piston rod (2.4) and the piston (2.6) may be moved by manually pushing the outer body (3.2) in a distal direction to perform an injection stroke, whereby a medication or drug contained in an inner cavity (2.1.2) of the pre-filled syringe is expelled through a hypodermic needle (2.3),