The invention relates to agricultural engineering, specifically to devices of the drive and rotation speed adjustment for a threshing rotor in a threshing separating device of rotary grain harvesters. The technical result, intended to be achieved by the invention, is an improvement in the reliability of the rotor drive due to its design simplification, an increase of torque transferred from the engine to the rotor and assured regulation of the speed of the stepless rotor. The specified technical result is obtained due to the fact that, in the arrangement of the grain harvester rotor drive, the system of rotor cleaning from blocking including hydraulic cylinder, ratchet wheel and lock is introduced, moreover, a hydraulic cylinder installed on the rotor drive gearbox housing controls lock blocking of the ratchet wheel by a mechanical linkage, and the ratchet wheel is fixed with a shaft of the inside planetary gear. Selection of transfer ratios for gearbox gears allows reducing the harvester weight due to the exclusion of the transmission gear box from the rotor drive gearbox.