According to the invention, a safety device (1) for a pre-filled syringe (2) comprises a hollow support body (1.2) having a releasable mounting means (1.2.6) adapted to mount a pre-filled syringe (2) within the support body (1.2), a hollow outer body (1.3) sildably arranged with respect to the support body (1.2) and adapted to receive the support body (1.2) and a release collar (1.4) non-rotatably arranged within the support body (1.2). The release collar (1.4) is movable relative to the support body (1.2) and adapted to release the mounting means (1.2.6). A guide track (1.2.4) is formed into at least one substantially planar side wall (1.2.1 ) of the support body (1.2). The release collar (1.4) comprises at least one flexible arm (1.4.5) with a guide pin (1.4.6) that extends from the flexible arm (1.4.5) and protrudes through the guide track (1.2.4). The guide pin (1.4.6) is movable within and along the guide track (1.2.4) in a plane defined by the substantially planar side wall (1.2.1). A guide rail (1.3.5) is formed into at least one substantially planar inner surface of the outer body (1.3). The guide rail (1.3.5) is adapted to abut against the guide pin (1.4.6) to guide the movement of the guide pin (1.4.6) along the guide track (1.2.4) when the outer body (1.3) is slid relative to the support body (1.2).
