PURPOSE: To enable the number of revolutions of the hydraulic motor of a working vehicle to be controlled regardless of engine speed by arranging a plurality of flow preference valves of different flow control rates between the hydraulic pump and the actuator of the working vehicle, and interposing a communication switching valve between the downstream side of one of the flow preference valves and the actuator.

CONSTITUTION: A hydraulic motor 18, which serves as an hydraulic actuator driven by means of operating oil from a hydraulic pump 11 connected directly to an engine 10, has an inflow port and a discharge port both of which are communicated with a two-position switching valve 17, and when the valve 17 serves as an open center, the hydraulic motor 18 is free regardless of the position of a three-way switching valve 16 and cannot rotate with its own power. When the two-position switching valve 17 is switched, the hydraulic motor 18 is connected to either a flow preference valve 14 or 15 which is selected by the three-way switching valve 16, and the specified amount of flow of operating oil is supplied to the hydraulic motor 18, and the hydraulic motor 18 rotates at a speed corresponding to the amount supplied, and then the oil discharged from the hydraulic motor 18 is forced to flow into a first hydraulic passage via a third hydraulic passage 19.