A refrigeration cycle apparatus in which a compressor, a condenser, an expansion device, and an evaporator are sequentially connected via refrigerant pipes to form a refrigeration cycle and in which a non-azeotropic refrigerant mixture circulates as a refrigerant circulating through the refrigeration cycle, the refrigeration cycle apparatus comprising: a detection path configured to bypass the refrigerant from a high-pressure side that is an outlet side of the condenser to a low-pressure side that is a suction side of the compressor and on which a pressure reducing device (8, 21) and a heating device (9, 22) are provided from the high-pressure side toward the low-pressure side; and a controller configured to control an operation of the refrigeration cycle, and to estimate a circulation composition that is a composition of the refrigerant circulating through the refrigerant cycle, wherein the heating device (9, 22) turns the refrigerant at an outlet side thereof into a superheated gas state, characterized in that the controller calculates an enthalpy at an inlet side of the pressure reducing device (8, 21) on the detection path, calculates an enthalpy at the outlet side of the heating device (9, 22) on the detection path, calculates an enthalpy difference of the refrigerant between the outlet side and an inlet side of the heating device (9, 22), calculates an enthalpy at an outlet side of the pressure reducing device (8, 21) by subtracting the enthalpy difference from the enthalpy at the outlet side of the heating device (9, 22), and estimates the circulation composition on the basis of the calculated enthalpy at the inlet side of the pressure reducing device (8, 21) and the calculated enthalpy at the outlet side of the pressure reducing device (8, 21). a detection path configured to bypass the refrigerant from a high-pressure side that is an outlet side of the condenser to a low-pressure side that is a suction side of the compressor and on which a pressure reducing device (8, 21) and a heating device (9, 22) are provided from the high-pressure side toward the low-pressure side; and a controller configured to control an operation of the refrigeration cycle, and to estimate a circulation composition that is a composition of the refrigerant circulating through the refrigerant cycle, wherein the heating device (9, 22) turns the refrigerant at an outlet side thereof into a superheated gas state, characterized in that the controller calculates an enthalpy at an inlet side of the pressure reducing device (8, 21) on the detection path, calculates an enthalpy at the outlet side of the heating device (9, 22) on the detection path, calculates an enthalpy difference of the refrigerant between the outlet side and an inlet side of the heating device (9, 22), calculates an enthalpy at an outlet side of the pressure reducing device (8, 21) by subtracting the enthalpy difference from the enthalpy at the outlet side of the heating device (9, 22), and estimates the circulation composition on the basis of the calculated enthalpy at the inlet side of the pressure reducing device (8, 21) and the calculated enthalpy at the outlet side of the pressure reducing device (8, 21). calculates an enthalpy at an inlet side of the pressure reducing device (8, 21) on the detection path, calculates an enthalpy at the outlet side of the heating device (9, 22) on the detection path, calculates an enthalpy difference of the refrigerant between the outlet side and an inlet side of the heating device (9, 22), calculates an enthalpy at an outlet side of the pressure reducing device (8, 21) by subtracting the enthalpy difference from the enthalpy at the outlet side of the heating device (9, 22), and estimates the circulation composition on the basis of the calculated enthalpy at the inlet side of the pressure reducing device (8, 21) and the calculated enthalpy at the outlet side of the pressure reducing device (8, 21).