PURPOSE: To make the economical operation of the compressor and prevent the damage of high stage side compressor by converting it to one-stage through switch- over of the magnetic valve control circuit at high vaporization range and to two- stage compressive refrigerator at low vaporization range.

CONSTITUTION: In the low vaporization temperature, the refrigerant from a vaporizer 5 flows like the continuous arrow through a three-way magnetic valve 6 of charging side, a low stage compressor 1 and a three-way magnetic valve 7. Then, the refrigerant meets together with the refrigerant from an intermediate cooler 4 to be charged to a high stage compressor 2 and be discharged. The discharged refrigerant is liquefied in a condenser 3 and one part is fed to the vaporizer 5 and the other to the intermediate cooler 4 to form the refrigerant cycle of two-stage compression refrigerator. In the high vaporization temperature, the three-way magnetic valve 6 of charging side, the three-way magnetic valve 7 and a magnetic valve 9 switched "On" and a magnetic valve 11 is switched "Off". Then, the refrigerant flows like the dotted arrow to form the refrigerant cycle of one-stage compression refrigerator