PURPOSE: To appropriately control a winch motor at its combined operation by increasing discharge capacity of the winch motor, before the total loading pressure of a hydraulic actuator and the winch motor reaches its maximum- capacity pressure.

CONSTITUTION: When hydraulic motors 3, 32 are placed in their complex operation, the discharge pressure of a hydraulic pump 1 is equal to the total pressure of consumption pressure of the hydraulic motor 32 and loading pressure of the hydraulic motor 3. When the total pressure is increased and an upper limit side pressure switch 40 reaches a set pressure, ON signal is output and signal S3 is output from a latching relay 42 to a relay 43 so as to excite 2 relay coil RS2. Power supply of the solenoid of a switching valve 12 is cut out thereby so as to be fixed at A position. Then, pilot pressure flowing from a switching valve 11 to a switching valve 15 is cut off by the switching valve 12 and the switching valve 15 is fixed at B position, so that pressure of the oil pressure 18a of a regulator 18 is released to a tank 9. Therefore discharge capacity of the hydraulic motor 3 is fixed at the maximum, even if the loading pressure is under the set pressure.