An air-conditioning apparatus comprising: a refrigeration cycle formed by connecting, with a refrigerant pipe, a compressor, a first refrigerant flow switching device, a first heat exchanger, a refrigerant passage of a second heat exchanger that exchanges heat between a non-azeotropic refrigerant mixture as a refrigerant and a heat medium, an expansion device that corresponds to the second heat exchanger, and a second refrigerant flow switching device; a heat medium circuit formed by connecting, with a heat medium pipe, a heat medium passage of the second heat exchanger and a use-side heat exchanger, the heat medium circuit being configured to circulate the heat medium different from the refrigerant; first temperature detecting means; second temperature detecting means, the first temperature detecting means and the second temperature detecting means being disposed before and after the expansion device; first pressure detecting means; second pressure detecting means, the first pressure detecting means and the second pressure detecting means being disposed before and after the expansion device; characterized in that the air-conditioning apparatus further comprises a computing device configured to calculate a composition of the refrigerant circulating in the refrigeration cycle on the basis of detection results of the first temperature detecting means, the second temperature detecting means, and the first pressure detecting means or the second pressure detecting means, wherein the computing device tentatively sets a value of a composition of the refrigerant circulating in the refrigeration cycle and outputs a physical property table corresponding to the set value, calculates a quality of the refrigerant flowing out of the expansion device on the basis of an inlet liquid enthalpy calculated on the basis of the physical property table and a temperature from the first temperature detecting means, and a saturated gas enthalpy and a saturated liquid enthalpy calculated on the basis of the physical property table and temperature information from the second temperature detecting means, calculates a liquid-phase concentration and a gas-phase concentration of the refrigerant flowing out of the expansion device on the basis of a detection result of the second temperature detecting means, a detection result of the first pressure detecting means and the physical property table, and calculates the composition of the refrigerant circulating in the refrigeration cycle on the basis of the quality calculated from the tentatively set value of the composition of the refrigerant circulating in the refrigeration cycle, liquid-phase concentration, and gas-phase concentration. a refrigeration cycle formed by connecting, with a refrigerant pipe, a compressor, a first refrigerant flow switching device, a first heat exchanger, a refrigerant passage of a second heat exchanger that exchanges heat between a non-azeotropic refrigerant mixture as a refrigerant and a heat medium, an expansion device that corresponds to the second heat exchanger, and a second refrigerant flow switching device; a heat medium circuit formed by connecting, with a heat medium pipe, a heat medium passage of the second heat exchanger and a use-side heat exchanger, the heat medium circuit being configured to circulate the heat medium different from the refrigerant; first temperature detecting means; second temperature detecting means, the first temperature detecting means and the second temperature detecting means being disposed before and after the expansion device; first pressure detecting means; second pressure detecting means, the first pressure detecting means and the second pressure detecting means being disposed before and after the expansion device; characterized in that the air-conditioning apparatus further comprises a computing device configured to calculate a composition of the refrigerant circulating in the refrigeration cycle on the basis of detection results of the first temperature detecting means, the second temperature detecting means, and the first pressure detecting means or the second pressure detecting means, wherein the computing device tentatively sets a value of a composition of the refrigerant circulating in the refrigeration cycle and outputs a physical property table corresponding to the set value, calculates a quality of the refrigerant flowing out of the expansion device on the basis of an inlet liquid enthalpy calculated on the basis of the physical property table and a temperature from the first temperature detecting means, and a saturated gas enthalpy and a saturated liquid enthalpy calculated on the basis of the physical property table and temperature information from the second temperature detecting means, calculates a liquid-phase concentration and a gas-phase concentration of the refrigerant flowing out of the expansion device on the basis of a detection result of the second temperature detecting means, a detection result of the first pressure detecting means and the physical property table, and calculates the composition of the refrigerant circulating in the refrigeration cycle on the basis of the quality calculated from the tentatively set value of the composition of the refrigerant circulating in the refrigeration cycle, liquid-phase concentration, and gas-phase concentration.