A device for preparing a high density briquette from culm and/or stem plants, especially for coupling to a tractor, intended for work directly in a field in a processing cycle including picking up a cut vegetable material, densification of it, forming a briquette in the form of an endless roll, cutting it to briquettes of standard lengths, passing and loading produced briquettes onto an associate wheeled means of transportation. The device comprises a pick-up, passing conveyors, a rolling unit comprised of rotary operating rolls, a cut off unit, a loading conveyor, a five-way gear, a power transmission system and a feeder of hydraulic circuits, and a frame. The rolling unit (5) comprises four rotary rolls (24), a rotary initiating mandrel (26), a torque meter (13), a five-way gear, an electronic controller with a set point device (15), an electromagnetic distributor (16), a two-side acting actuator (21). Increase of the range and accuracy of operating parameters' settings, that is the magnitude of the densification degree of a material roll formed by the rolling unit, as a result of application of the torque meter as a source of the signal about the real resistance torque on the gear shaft has been achieved.