PURPOSE: In a compressor for cooling refrigerator and cabin of rolling stock, to prevent liquid compression thus to protect the compressor by unclutching when the compressor temperature is lower than that of other system in regrigerating cycle and the engine rotation is higher than setting level.

CONSTITUTION: When the compressor temperature 10 drops by setting temperature (K) than the evapolator temperature 11, a comparator 12 will provide a lock signal (L) to a switch circuit 21. If the engine rotation 22 is higher than 1,200 rpm, said circuit 21 will turn on to turn off a control switch 15 through a magnet clutch drive circuit 13 to stop power supply thus to stop the compressor and to light a lamp 16 through lamp lighting circuit 14 and switch 17. With such arrangement, driving under refrigerant liquid feeding state of compressor is prevented to protect the compressor.