A displacement adjustment device (100) for at least partly converting a rotation into a translation, comprising: a rotation input member (114) which is bearing-mounted so as to be rotatable but axially secured relative to a frame said rotation input member (114) being provided with a hollow (116) extending axially therethrough; a bar (11) positioned in the hollow (116) and having its outside surface provided with a screw thread (17), means (12) being prvided for preventing rotation of said bar (11) relative to a frame; and a coupling gear wheel (120) arranged for rotation in the rotation input member (114), wherein the axis of rotation of the coupling gear wheel (120) is substantially perpendicular to the axis of rotation input member (114), wherein the coupling gear wheel (120) has teeth (121) engaging with the screw thread (17) of the bar (11) and, wherein the rotation bearing of the coupling gear wheel (120) comprises a slip coupling (130) relative to the rotation input member (114). An example of an application of such a device is in a mirror adjusting instrument of a vehicle.