For securing the position of the conveyor belt when starting the belt under load, a belt tensioning device, has a circulating conveyor belt, carrying idlers arranged between the carrying run and the return run of the conveyor belt, a drive mechanism, a power transmission device for moving the conveyor belt, a gear ring and a toothed belt for power transmission, the gear ring being allocated to the power transmission device and the toothed belt being allocated to the conveyor belt, wherein a guiding component part adapted to the edge area of the circulating conveyor belt and a contacting component part for direct contact with the surface of the conveyor belt are provided, and wherein the contacting component part is arranged inside the guiding component part.