According to the invention a safety device (1) for a pre filled syringe (2) comprises a hollow support body (1.2) for mounting the pre filled syringe (2) therein a hollow needle shield (1.1) that is slidable relative to the support body (1.2) and guiding means for guiding the movement of the needle shield (1.1) relative to the support body (1.2). The guiding means comprise a flexible arm (1.1.4) with a guide pin (1.1.3) a guide track (1.2.5) and a separating wall (1.2.6). The guide pin (1.1.3) extends from the flexible arm (1.14) in a radial direction and protrudes into the guide track (1.2.5). The separating wall (1.2.6) extends into the guide track (1.2.5) in a direction parallel to a central axis (A) of the safety device (1). When the needle shield (1.1) is slid relative to the support body (1.2) the guide pin (1.1.3) moves along the guide track (1.2.5) to deflect the flexible arm (1.1.4) in a lateral direction (L) perpendicular to the central axis (A) and the movement of the guide pin (1.1.3) along the guide track (1.2.5) is guided by the interplay of the flexible arm (1.1.4) and the separating wall (1.2.6).
