FIELD: fifth wheel tractors. SUBSTANCE: invention relates to fifth wheel tractors. Trolley for towing a semi-trailer with a device for stabilizing rectilinear motion contains a frame connected by its lower part to the axle of the running wheels, and by its upper part connected to the semi-trailer frame by means of a king pin and a fifth wheel coupling. The fifth wheel coupling includes a base plate made in the form of a reference turning circle containing an angular slot made in the form of a sector. A telescopic mechanism is installed on the lower part of the semi-trailer frame, consisting of two links - an outer hollow link fixed motionlessly on the semi-trailer frame, and an inner link inserted inside the outer link from the side of the slewing circle. A compression spring is installed between the inner and outer links of the telescopic mechanism. At the free end of the inner link, a rotating pressure roller is fixed by means of a vertical axis. EFFECT: reduction of transverse lateral oscillations of the semi-trailer is achieved when driving on rectilinear trajectories due to the formation of a force stabilizing moment relative to the pivot of the semi-trailer, which contributes to the straightness of the movement of the rolling cart and the semi-trailer. 1 cl, 3 dwg.