A refrigeration cycle apparatus comprising: a refrigeration cycle including a compressor configured to suck, compress and discharge a refrigerant, the refrigeration cycle allowing the refrigerant discharged from the compressor to be returned to the compressor through a condenser, an expansion valve and an evaporator; and an opening control section configured to control a degree of opening of the expansion valve such that a degree of superheating of the evaporator is at a target value; characterized by comprising a leakage detect section configured to predict, based on a quantity of change in state of the refrigeration cycle, a degree of opening of the expansion valve to be attained at a current stage of operation of the refrigerant cycle on the premise that the refrigerant is not leaked from the refrigeration cycle, and to detect leakage of the refrigerant in the refrigeration cycle by comparing the predicted degree of opening with an actual degree of opening, whereby said quantity of change in state is a difference between a state quantity at beginning of operation of the refrigeration cycle and a state quantity at a current stage of operation of the refrigeration cycle, said state quantity at beginning of operation of the refrigeration cycle is at least one of an operating frequency Fx of the compressor, and a condensation temperature Tcx, an evaporation temperature Tex and a degree of superheating SHx of the refrigeration cycle, and said state quantity at the current stage of operation of the refrigeration cycle is at least one of an operating frequency Fa of the compressor, and a condenser temperature Tca, an evaporator temperature Tea and a degree of superheating SHa at the current stage of operation of the refrigeration cycle. a refrigeration cycle including a compressor configured to suck, compress and discharge a refrigerant, the refrigeration cycle allowing the refrigerant discharged from the compressor to be returned to the compressor through a condenser, an expansion valve and an evaporator; and an opening control section configured to control a degree of opening of the expansion valve such that a degree of superheating of the evaporator is at a target value; characterized by comprising a leakage detect section configured to predict, based on a quantity of change in state of the refrigeration cycle, a degree of opening of the expansion valve to be attained at a current stage of operation of the refrigerant cycle on the premise that the refrigerant is not leaked from the refrigeration cycle, and to detect leakage of the refrigerant in the refrigeration cycle by comparing the predicted degree of opening with an actual degree of opening, whereby said quantity of change in state is a difference between a state quantity at beginning of operation of the refrigeration cycle and a state quantity at a current stage of operation of the refrigeration cycle, said state quantity at beginning of operation of the refrigeration cycle is at least one of an operating frequency Fx of the compressor, and a condensation temperature Tcx, an evaporation temperature Tex and a degree of superheating SHx of the refrigeration cycle, and said state quantity at the current stage of operation of the refrigeration cycle is at least one of an operating frequency Fa of the compressor, and a condenser temperature Tca, an evaporator temperature Tea and a degree of superheating SHa at the current stage of operation of the refrigeration cycle.