PURPOSE: To preferentially actuate an actuator on the side of a first circuit system by preventing discharge oil of a first pump of the circuit system from being supplied to a second circuit system except for direct advance running.

CONSTITUTION: A parallel passage 10 of a first circuit system and a parallel passage 32 of a second circuit system are communicated through to each other through a cofluence control valve V at the time of confluence control. Additionally, they are constituted so as to shut off the communication at another time so that discharge oil of a first pump P1 connected to the first circuit system is not supplied to the second circuit system. Thereby, except for the time when confluence is controlled, an actuator of a change-over valve connected to the parallel passage 10 of the first circuit system is preferentially actuated, and it is devised that even when an actuator on the side of the second circuit system is a light load, no influence is affected on actuation of the actuator on the side of the first circuit system.