PURPOSE: To exactly compensate for the flow rate of fluid all the time regardless of the variation in the loads of other actuators for the actuator for a rotator by providing a pressure compensation valve capable of alternately controlling both pressure control sections for throttling and diversion.

CONSTITUTION: A pressure compensation valve 10 capable of alternately controlling a control section Y for throttling pressure and a control section Z for diversion pressure is provided on the discharge side of a fluid pump 1. An actuator 3 for a slewing body is connected through a flow direction control valve 30 to the rear position of the control section Y, and the rear position of a flow regulating and varying orifice 40 is led to the spring side. Other actuators 4 and 4' are connected through direction control valves 5 and 5' to the rear position of the control section Z. By the compensation valve 10, both the control sections Y and Z are alternately controlled for mutual variations of loads W1 and W2, and thereby compensation for the flow rate to the actuator 3 is preferentially made. Since the speed of the actuator 3 is not varied even when loads are changed during the slewing period of the slewing body of a power shovel, the operability of the construction machine is excellent and the possibility of occurrence of hazard during the operations is reduced.