According to the present disclosure, a safety device (1) for a pre-filled syringe (2) comprises a hollow outer body (1.3) receiving a support body (1.2) having two side walls opposing each other, wherein the outer body (1.3) slides relative to the support body (1.2) to inject a medication contained in a pre-filled syringe through a hypodermic needle and to release and retract the pre-filled syringe retained within the safety device, wherein a guide track (1.2.4) is formed into at least one side wall (1.2.1) of the support body (1.2), a guide rail (1.3.5) is formed into at least one inner surface of the outer body (1.3) facing the side wall of the support body with the guide track, a guide pin (1.4.6) is movable within and along the guide track (1.2.4) in a plane defined by the side wall (1.2.1) when the outer body (1.3) is slid relative to the support body (1.2), and the guide pin (1.4.6) is prevented from returning to its start position by the guide rail (1.3.5) so that a re-usage of the safety device is prevented.
