The unit (38) has driven pulleys, a drive pulley and a tension roller, where each driven pulley is connected to each rotation shaft of cutting disks (34-1, 34-4). Belts ensure transmission between a hydraulic actuators (36) and rotation shafts. Each hydraulic actuator is positioned in rear of rotation shafts of cutting disks, where the shafts of the cutting disks are arranged along a curve line. One of the belts is cooperated with the drive pulley and driven pulleys. The cutting disks are arranged with a cutting superposition.
