HEAT PUMP CYCLE

A refrigerant shortage determination unit (S2, S3, S6, S8, S9) determines that refrigerant is in shortage state if a high pressure side refrigerant pressure (Pd) between a discharge port of a compressor (11) and an inlet of a decompression unit (13) is lower than a predetermined first reference pressure (KPd1) when an outside air temperature (Tam) is equal to or higher than a predetermined reference outside air temperature (KTam), and determines that refrigerant is in shortage state if the high pressure side refrigerant pressure (Pd) is lower than a predetermined second reference pressure (KPd2) in a state where the compressor (11) is operated when the outside air temperature (Tam) is lower than the reference outside air temperature (KTam). A compressor control unit (S4) reduces a refrigerant discharge capacity of the compressor (11) when the refrigerant shortage determination unit determines that refrigerant is in the shortage state.