PURPOSE: To improve the workability of a hydraulic working machine by making the operating speed and speed ratio of the working machine coincident with the manipulated variable and operation ratio of an operation command section.

CONSTITUTION: When a working machine is operated, the manipulated variable of the machine and the data detected by means of a boom speed detector 115a and a dipper stick speed detector 115b are inputted to a working operation command section 75. Then a controller 85 makes calculation based on the data and an engine 25 is driven in accordance with the signal value of the controller 85. Successively, first and second variable capacity hydraulic pumps 35a and 35b are controlled to supply a summed flow rate proportional to the manipulated variable of the command section 75 by means of first and second electromagnetic proportional valves 45a and 45b. Moreover, first and second electromagnetic proportional control valves 95a and 95b control the flow rates of the fluids supplied to a dipper stick cylinder 105a and a boom cylinder 105b so that the flow rates may become coincident with the manipulated variable and operation ratio of the command section 75. Therefore, the operability and working efficiency of the working machine can be improved regardless of the working environment and the fluctuation of the load pressure.