Actuating device for moving a helicopter tail part, the device comprising: - a first part comprising a first casing intended to be fixed to a frame of the helicopter, a first element mounted in rotation with respect to the first casing and a first motor (11a, 11b) able to rotate the first element, characterised in that it comprises - a second part, mobile with respect to the first part, comprising a second casing intended to be fixed to the tail part, a second element mounted in rotation with respect to the second casing and a second motor able to rotate the second element in rotation, - a connecting element to connect the first part with the second part, the connecting element: o being mobile in translation with respect to the first element the connecting element forming with the first element a screw and a nut, in such a way that a rotation of the first element with respect to the connecting element causes a translation of the connecting element with respect to the first element, and o being mobile in translation with respect to the second element, the connecting element forming with the second element a screw and a nut, in such a way that a rotation of the second element with respect to the connecting element causes a translation of the connecting element with respect to the second element, wherein the first element and the second element are two nuts, and the connecting element forms a screw coupled to each nut (13, 23). - a first part comprising a first casing intended to be fixed to a frame of the helicopter, a first element mounted in rotation with respect to the first casing and a first motor (11a, 11b) able to rotate the first element, characterised in that it comprises - a second part, mobile with respect to the first part, comprising a second casing intended to be fixed to the tail part, a second element mounted in rotation with respect to the second casing and a second motor able to rotate the second element in rotation, - a connecting element to connect the first part with the second part, the connecting element: o being mobile in translation with respect to the first element the connecting element forming with the first element a screw and a nut, in such a way that a rotation of the first element with respect to the connecting element causes a translation of the connecting element with respect to the first element, and o being mobile in translation with respect to the second element, the connecting element forming with the second element a screw and a nut, in such a way that a rotation of the second element with respect to the connecting element causes a translation of the connecting element with respect to the second element, o being mobile in translation with respect to the first element the connecting element forming with the first element a screw and a nut, in such a way that a rotation of the first element with respect to the connecting element causes a translation of the connecting element with respect to the first element, and o being mobile in translation with respect to the second element, the connecting element forming with the second element a screw and a nut, in such a way that a rotation of the second element with respect to the connecting element causes a translation of the connecting element with respect to the second element,