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