A locking device is disclosed for locking a cap on a container with a flange including a lid housing a bushing provided with lower inner notches supported under the flange and outer notches engaging with a groove in the lid to secure the bushing to the lid, the lid including a severable frangible zone, the bushing being formed by a ring extended by lugs intended to surround the cap and provided with at least one deformable and severable bridge provided opposite the lugs and capable of being elastically deformed radially to allow the forced insertion of the flange into the bushing and of being broken to allow the removal of the bushing relative to the flange followed by the removal of the cap from the container.