According to the invention, a safety device (1) for a pre-filled syringe (2) comprises a hollow support body 1.2) for retaining the pre-filled syringe (2), a hollow needle shield (1.1) that is movable relative to the support body (1.2) from a first position(I) to a second position (II), releasable mounting means(M) to mount the pre-filled syringe (2) within the support body (1.2) and a spring means (1.4) arranged within the support body(1.2) in a non-energized or only slightly energized state. The movement of the needle shield (1.1) from the first position(I) to the second position(II) fully energizes the spring means (1.4).
