The invention relates to a safety device (S) for a drug delivery device (1), comprising: —a support body (2) adapted to receive and hold the drug delivery device (1), —a needle shield (8) slidably arranged relative to the support body (2), —an inner locking mechanism (12) arranged inside the needle shield (8) between a front end of the needle shield (8) and a front end of the support body (2) and adapted to lock and unlock the needle shield (8).