PURPOSE: To secure composite operability of an actuator and obtain energy- saving performance of a hydraulic driving device which has a plurality of actuators.

CONSTITUTION: Auxiliary valves 52, 54 are provided on tank lines 36, 38 of directional changeover valves 24, 26. A specified signal is applied to the auxiliary valves 52, 54 by means of load pressure detecting means (unit signal pressure lines 44, 46) and a maximum pressure selecting means (maximum signal pressure line 50) provided on each of the directional changeover valves, and thereby a composite operation device 56 is structured. On the other hand, there are provided a pressure compensation flow rate valve 72 for the application of the maximum signal pressure line 50 and a bypass flow rate detecting means 74 having a means 76 which applies a control signal to a discharge flow rate control means 10 on a bypass line 58 provided on a pump discharge line 14. Thus, a pump flow rate control device 70 which reduces a pump discharge flow rate in respect to increasing of the bypass flow rate.