PURPOSE: To improve safety of the circuit in the caption by breaking pressure supply from a pilot pump to solenoid valves with operation lever set in the neutral position.

CONSTITUTION: Between a pilot pump 3 and solenoid valves 5aW5c, 6aW6c, there is provided a switching valve 21 which breaks pressure supply from the pilot pump 3 to the solenoid valves 5aW5c, 6aW6c with an operation lever 7 set in the neutral position. Thereby, it is possible to securely prevent a control valve 4 from generating mis-operation caused by the sticks or the like of the solenoid valves 5aW5c, 6aW6c due to noise, interference, dust etc., with the operation lever 7 set in the neutral position. Therefore, it is possible to prevent an actuator from operating against an operator's will with the operation lever 7 set in the neutral position, so as to improve safety.