PURPOSE: To make a clutch independently function through one hydraulic circuit to accurately control the clutch by providing the hydraulic circuit behind a flow dividing valve with a directional control valve to change over a pressure oil to a pressure control valve for clutch working oil pressure and a power take off working valve or a travel working valve, and a pressure guaranteeing valve between the directional control valve and the flow dividing valve.

CONSTITUTION: A pressure oil fed through a flow dividing valve 2 from a hydraulic pump 1 is introduced directly or through a pressure guaranteeing valve 3 into a directional control valve 4 to change over the communication of the pressure oil with clutches 7, 10. The valve 4 makes a circuit 18 communicate with a travel working valve 9 and a pressure control valve 8, and changes over a circuit 19 to a power take off guaranteeing position 23 where the circuit 19 communicates with a power take off working valve 5 and a pressure control valve 6 and a travel guaranteeing position 24 having a connection reverse to the above-mentioned one. The pressure control valve 6 controls the oil pressure to that preset by a control device according to the clutches 7, 9. The clutches 7, 9 can therefore be independently operated through only one hydraulic circuit to simply execute the accurate control of the clutches and the formation of the hydraulic circuit.