A retarding device insertable between two members connected to rotate relatively about a hinge axis, and which opposes and so retards such rotation in predetermined manner; the device having: a substantially cylindrical support carried integrally by a first of the rotationally connected members and substantially coaxial with the hinge axis; a coil, spring fitted interferentially to the support and terminating with two opposite radial arms projecting towards a second of said members connected to each other for relative rotation; and a retaining seat carried integrally by the second member and on which the arms of the spring rest, on opposite sides, and are stressed by the second member, as a consequence of the aforementioned relative rotation, to deform the spring in such a direction as to progressively reduce and, beyond a certain point of the moving path of the other member, substantially eliminate, the interference with which the spring is fitted to the support. The rotation of the rotationally connected members is broken in a predetermined manner.