CASCADE HEAT PUMP CYCLE

PROBLEM TO BE SOLVED: To provide a cascade heat pump cycle capable of keeping the almost same flow rate of a refrigerant in each refrigerant circuit regardless of a high load condition and a low load condition, keeping a compression ratio of each compressor at a prescribed value or more in the low load condition, and securing reliability.SOLUTION: A compressor control mechanism 5 controls a high-stage compressor 21 so that a measured hot water supply temperature measured on a water medium, becomes equal to a set hot water supply temperature, and controls a low-stage compressor 11 so that a measured intermediate parameter as a pressure or a temperature measured on a low-stage refrigerant or a high-stage refrigerant in a cascade heat exchanger C, becomes equal to a target intermediate parameter determined for each of combinations of a hot water supply temperature as a measured hot water supply temperature or a set hot water supply temperature, and an outside air temperature.