Abstract: In a reduction unit of a drilling motor comprising a casing, input and output shafts installed on supports, a reduction gear including sun and crown wheels, pinion carriers and planet pinions with supports located in a circular space between the wheels, an oil-filled chamber and a system of oil protection, there is provided a means eliminating the overloading of the reduction gear and a means eliminating the effect of torque fluctuations on the operation of the reduction gear while the supports of the input and output shafts installed on the ends of said shafts connected with the reduction gear are made in the form of articulated units taking axial loads and permitting angular displacements of the shafts, each of said shafts carrying a seal installed side by side with said support at the side opposite to the reduction gear, said seal being provided with a dividing space filled with a buffer fluid which protects said seal against contact with the drilling fluid.