A refrigeration cycle apparatus (100, 200, 300) comprising: a heat source unit including a compressor, a heat-source-side heat exchanger, an expansion valve (5, 6, 16), and a liquid reservoir; an indoor unit including an indoor-side heat exchanger; and a hot water supply unit including a water heat exchanger, the heat source unit and the indoor unit being connected together by indoor-side extension pipes including an indoor-side liquid extension pipe and an indoor-side gas extension pipe, and the heat source unit and the hot water supply unit being connected together by hot-water-supply-side extension pipes including a hot-water-supply-side liquid extension pipe and a hot-water-supply-side gas extension pipe, wherein the refrigeration cycle apparatus performs a cooling and hot water supply simultaneous operation in which the indoor-side heat exchanger serves as an evaporator, the water heat exchanger serves as a condenser, cooling energy is supplied from the indoor-side heat exchanger, and heating energy is supplied from the water heat exchanger, a heating operation in which the heat-source-side heat exchanger serves as an evaporator and the indoor-side heat exchanger serves as a condenser, and heating energy is supplied from the indoor-side heat exchanger, and a cooling operation in which the indoor-side heat exchanger serves as an evaporator, the heat-source-side heat exchanger serves as a condenser, and cooling energy is supplied from the indoor-side heat exchanger, wherein an internal volume of the heat-source-side heat exchanger is larger than an internal volume of the indoor-side heat exchanger and larger than an internal volume of the water heat exchanger, and wherein an internal volume of the liquid reservoir is determined in accordance with an excess refrigerant amount which is a difference between a minimum amount of refrigerant necessary for the cooling operation and a minimum amount of refrigerant necessary for the heating operation, and characterised in that a ratio of an internal volume of the hot-water-supply-side liquid extension pipe to the internal volume of the water heat exchanger is set to be equal to or more than a ratio of a minimum internal volume of the hot-water-supply-side liquid extension pipe to the internal volume of the water heat exchanger, and the minimum internal volume of the hot-water-supply-side liquid extension pipe is set such that a minimum amount of refrigerant necessary for the cooling and hot water supply simultaneous operation is equal to the minimum amount of refrigerant necessary for the heating operation. a heat source unit including a compressor, a heat-source-side heat exchanger, an expansion valve (5, 6, 16), and a liquid reservoir; an indoor unit including an indoor-side heat exchanger; and a hot water supply unit including a water heat exchanger, the heat source unit and the indoor unit being connected together by indoor-side extension pipes including an indoor-side liquid extension pipe and an indoor-side gas extension pipe, and the heat source unit and the hot water supply unit being connected together by hot-water-supply-side extension pipes including a hot-water-supply-side liquid extension pipe and a hot-water-supply-side gas extension pipe, wherein the refrigeration cycle apparatus performs a cooling and hot water supply simultaneous operation in which the indoor-side heat exchanger serves as an evaporator, the water heat exchanger serves as a condenser, cooling energy is supplied from the indoor-side heat exchanger, and heating energy is supplied from the water heat exchanger, a heating operation in which the heat-source-side heat exchanger serves as an evaporator and the indoor-side heat exchanger serves as a condenser, and heating energy is supplied from the indoor-side heat exchanger, and a cooling operation in which the indoor-side heat exchanger serves as an evaporator, the heat-source-side heat exchanger serves as a condenser, and cooling energy is supplied from the indoor-side heat exchanger, wherein an internal volume of the heat-source-side heat exchanger is larger than an internal volume of the indoor-side heat exchanger and larger than an internal volume of the water heat exchanger, and wherein an internal volume of the liquid reservoir is determined in accordance with an excess refrigerant amount which is a difference between a minimum amount of refrigerant necessary for the cooling operation and a minimum amount of refrigerant necessary for the heating operation, and characterised in that a ratio of an internal volume of the hot-water-supply-side liquid extension pipe to the internal volume of the water heat exchanger is set to be equal to or more than a ratio of a minimum internal volume of the hot-water-supply-side liquid extension pipe to the internal volume of the water heat exchanger, and the minimum internal volume of the hot-water-supply-side liquid extension pipe is set such that a minimum amount of refrigerant necessary for the cooling and hot water supply simultaneous operation is equal to the minimum amount of refrigerant necessary for the heating operation.