PURPOSE: To reduce the size of solenoid valve by providing a regulator for reducing the variation of pressure in front of solenoid valve thereby suppressing the amount of refrigerant to be controlled by the solenoid valve.
CONSTITUTION: Upon sufficient cooling in the cabin to overload the compressor, a signal is fed from a temperature sensor in the cabin to a solenoid valve 15 to open a valve 15 thus to discharge high pressure refrigerant from a compression chamber (A) through the solenoid valve 15 and first branch 101 into a suction chamber (B). Consequently, pressure in the control chamber 21 will drop to move a spool 19 thus to open a bypass port 18 communicating between said chambers (B) and (A) and to reduce the delivery capacity. The pressure to be applied into the control chamber 21 in accordance to the load condition will increase and if it can not be released only through the solenoid valve 15, a regulator 23 will function to release high pressure refrigerant through the solenoid valve 15 and regulator 23. Consequently, the amount of refrigerant to be released through the solenoid valve 15 can be suppressed resulting in reduction of size of solenoid valve 15.