PURPOSE:To take out an increased input revolution by turning a motor using a pressurized fluid from a pump while utilizing the pressurized fluid recirculatedly in the titled unit used for driving mechanism of a rolling stock. CONSTITUTION:A variable space 6 and 7 are formed in a cylinder 4 of a pump 1 where a dual-headed piston 5 is arranged in a manner to make a free sliding therein, and a rotor 18 is fixed to an output shaft 17 of a motor 2 with a number of vanes 19 being attached to it. And an eccentric pin 10 of a gear 9 arranged outside of the cylinder 4 is fitted into a long hole 8 arranged in a radial direction of the piston 5 so that a power can be tansmitted to a pinion 11 to turn the gear 9 and then to give the piston 5 a reciprocating motion. Accordingly, a pressurized fluid such as oil etc. which is filling the both rooms 6 and 7 of the pump 1 flows in to the moter 2 via an outlet 13, passageway 21, and flow inlet 20 and after turning the output shaft 17 through the vanes 19 and the rotor 18, flows into the both rooms 6, and 7 again via outlet 22, passageway 23, and inlet 15.