PURPOSE: To prevent the device from conducting a malfunction at starting, by a method wherein motor-operated sluice valves are separately located on an oil discharge pipe and on an oil feed pipe respectively, and an amount of oil, which dissolves in coolant at a stopping time, decreases through the disconnection of an oil feed system from a compression system while the device is not in operation.

CONSTITUTION: A motor-operated sluice valve 12 is located around the middle of an oil discharge line 8, and a motor-operated valve 13 around the middle of an oil feed line 7. When a compressor stops working, the two motor-operated sluice valves 12 and 13 are completely closed in synchronism with the stoppage of the compressor 5. The motor-operated sluice valve 12 is caused to close later than the motor-operated sluice valve 13 so that the valve 12 is closed fully after oil discharge from a gear box 10 is completed. The disconnection of the oil feed system from the compression system permits the reduction in an oil amount which dissolves in coolant, and thus the malfunction at the starting is prevented. Additionally, when the compressor starts, the motor-operated sluice valves 12 and 13 are first closed completely, the oil pump 2 then starts and the compressor 5 starts after oil starts to be fed to a gear box 10.