The device for preparing a high density briquette from culm and/or stem plants, especially for coupling to a tractor, comprising a pick-up 9, passing conveyors 8, a rolling unit 5 comprised of a rotary operating rolls 24, a cut off unit 6, a loading conveyor 7, a five-way gear 4, a power transmission system and a feeder of hydraulic circuits 19, and a frame 1, wherein the rolling unit 5 comprises four rotary rolls 24 with outer working surfaces in the form of truncated cone, located on one side in a plate 29 in a body 25, and on the other side in a turn-table 22 of the body 25, and comprises a rotary initiating mandrel 26 with a pivot set in a seating of a bearing in the plate 29 in the body 25, situated in a central centre line, and furthermore, seatings of adjustable bearings 23 are located in the plate 29 in the body 25, on the circumference of a circle with a diameter D 1, located symmetrically by the angle of 90 degree, in which pivots of the rotary rolls 24 with the outer working surfaces in the form of truncated cone are set, whereas the body 25 is equipped with an opening with a diameter D k, in which the turn-table 22 is set, which allows an angular position change in the range of angle from 0 degree to 20 degree, perpendicularly to the central centre line, while seatings of bearings 23 are located in the turn-table 22, on the circumference of a circle with a diameter D 2, located symmetrically by the angle of 90 degree, in which pivots of the rotary rolls 24 with the outer working surfaces in the form of truncated cone are set, and furthermore, the turn-table 22 has a centrally located through hole 27 through which a finished product in the form of an endless briquette 30 is transferred, whereas the rolling unit 5 comprises a torque meter 13 with an input shaft connected with an output of a main gear 2 receiving drive from a power take-off shaft, and an output shaft of the torque meter 13 is connected with an input shaft of the five-way gear 4, while outputs of the five-way gear 4, from the first one to the fourth, are connected via a flexible coupling or an articulated joint 28 with shafts, from the first one to the fourth, of the rotary rolls 24 with the outer working surfaces in the form of truncated cone, and the fifth output of the five-way gear 4 is connected via a coupling or an articulated joint 28 with a shaft of the rotary initiating mandrel 26 in the form of truncated cone, while the rolling unit 5 comprises an electronic controller 15 with a set point device, an input of which is connected with a signal output of the torque meter 13, whereas an output of the electronic controller 15 with the set point device is connected with an input of an electric circuit of an electromagnetic distributor 16, while an input of an hydraulic circuit of the electromagnetic distributor 16 is connected with a hydraulic circuits' feeder 19, and a first output of the hydraulic circuit of the electromagnetic distributor 16 is connected with a first input of a two-side acting actuator 21, whereas a second output of the hydraulic circuit of the electromagnetic distributor 16 is connected with a second input of the two-side acting actuator 21, and furthermore, the two-side acting actuator 21 is connected with the body 25, while a piston rod end of the two-side actuator 21 is articulately connected with a connector set in the turn-table 22.