604079 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 within the support body, a hollow outer body (1.3) sildably arranged with respect to the support body and adapted to receive the support body and a release collar (1.4) non-rotatably arranged within the support body. The release collar is movable relative to the support body and adapted to release the mounting means. A guide track (1.2.4) is formed into at least one substantially planar side wall (1.2.1 ) of the support body. The release collar comprises at least one flexible arm (1.4.5) with a guide pin (1.4.6) that extends from the flexible arm and protrudes through the guide track. The guide pin is movable within and along the guide track in a plane defined by the substantially planar side wall. A guide rail (1.3.5) is formed into at least one substantially planar inner surface of the outer body. The guide rail is adapted to abut against the guide pin to guide the movement of the guide pin along the guide track when the outer body is slid relative to the support body.
