Abstract: The disclosure relates to a device for locking the lids or covers of wells and similar constructions, a locking mechanism which is actuable from the outside being disposed on the underside of the cover.The novel feature of the invention is that the locking device comprises at least one lever serving as a locking arm and engaging with the wall of the well. These arms are of such length in relation to the size of the well opening and of such inclination in position of engagement with the walls of the well that, on attempts to lift the cover, the locking arms or levers will be urged against the walls of the well with increased force in relation to the lifting force. Furthermore, the locking device is of such a nature that it is self-locking when the cover is put in place but must be deactuated prior to removal of the cover.