According to the invention, a safety device(1) for a pre-filled syringe(2) comprises - a support body(1.3) adapted to mount the pre-filled syringe(2), - a first needle shield(1.1) slidably arranged with respect to the support body(1.3) and - a second needle shield(1.2) slidably arranged with respect to the support body(1.4) and releasably retained in a retracted position(PR). A proximal movement of the first needle shield(1.1) with respect to the support body(1.3) releases the retention of the second needle shield(1.2) in the retracted position(PR), so that the second needle shield(1.2) is allowed to slide in the distal direction towards an advanced position(PA).
