PURPOSE: To attempt to reduce starting load and make the reduced voltage starting easy by feeding lubricating oil in the minimum necessary quantity from an oil cooler to the compressor main body side for the reduced voltage time only at the time of low temperature starting and blocking and forcibly unloading a suction valve.

CONSTITUTION: The temperature of lubricating oil inside an oil separator 4 is detected by a resistance temperature sensor 18 at the starting time of a compressor 2 and sent to a temperature controller 17. And, when it is below a set temperature, a command is sent to a modular roll motor 18 to close between the A-B ports of an oil regulating valve 8 at the starting time of the compressor 2, and restricts the oil quantity fed to the main body side of the temperature 2 at the minimum necessary quantity until the time when reduced voltage is released. Also, a three-way electromagnetic valve 11 is demagnetized to close between the A-B ports of the electromagnetic valve 11 and further open between the A-C ports at the starting time of the compressor 2. Next, the self pressure of the compressor 2 is introduced to an unload room 13 through the separator 4, thence a pipe 11' → the A-C ports of the electromagnetic valve 11 → a pipe 10' to block and forcibly unload a suction valve 1.