To increase the maximum speed of a vehicle by reduce loss of horsepower in a hydrostatic transmission for vehicle running, and reducing this horsepower loss due to stirring resistance in case of a hydraulic motor and a speed reducer rotated at a high speed in particular.

This hydrostatic transmission for vehicle running is so constituted that a hydraulic pump 5 to be driven by an engine mounted on a vehicle is set up in the upper part of the inside of an integral casing 8 whose internal space communicated, while a gear reducer 7 connected to a propeller shaft of this vehicle is set up in the lower part of the inside of this casing 8, and a hydraulic motor 6 being connected to the hydraulic pump 5 via a closed hydraulic circuit and driving the gear reducer 7, is set up in an intermediate position between the hydraulic pump 5 and the gear reducer 7 in the casing 8, and then a tank collecting leakage oil of the hydraulic pump 5 is installed in a height position where an oil level position in the casing 8 is lower than a rotating part of the hydraulic motor 6 and impregnates a rotating part of the gear reducer 7.