A refrigeration cycle apparatus comprising: a refrigerant circuit that includes a compressor , a heat source-side heat exchanger , an expansion mechanism , and a usage-side heat exchanger , wherein, in the refrigerant circuit, a refrigerant containing at least 1,2-difluoroethylene (HFO-1132 (E)) is sealed, and wherein, at least during a predetermined operation, in at least one of the heat source-side heat exchanger and the usage-side heat exchanger, a flow of the refrigerant and a flow of a heating medium that exchanges heat with the refrigerant are counter flows, characterized in that the refrigerant comprises HFO-1132(E), R32, and R1234yf, wherein when the mass% of HFO-1132(E), R32, and R1234yf based on their sum in the refrigerant is respectively represented by x, y and z, coordinates (x,y,z) in a ternary composition diagram in which the sum of HFO-1132(E), R32, and R1234yf is 100 mass% are within the range of a figure surrounded by line segments ON, NU, and UO that connect the following 3 points: point O (22.6, 36.8, 40.6), point N (27.7, 18.2, 54.1), and point U (3.9, 36.7, 59.4), or on these line segments; the line segment ON is represented by coordinates (0.0072y 2 -0.6701y+37.512, y, -0.0072y 2 -0.3299y+62.488); the line segment NU is represented by coordinates (0.0083y 2 -1.7403y+56.635, y, -0.0083y 2 +0.7403y+43.365); and the line segment UO is a straight line, and the refrigerant comprises HFO-1132(E), R32, and R1234yf in a total amount of 99.5 mass% or more based on the entire refrigerant. a refrigerant circuit that includes a compressor , a heat source-side heat exchanger , an expansion mechanism , and a usage-side heat exchanger , wherein, in the refrigerant circuit, a refrigerant containing at least 1,2-difluoroethylene (HFO-1132 (E)) is sealed, and wherein, at least during a predetermined operation, in at least one of the heat source-side heat exchanger and the usage-side heat exchanger, a flow of the refrigerant and a flow of a heating medium that exchanges heat with the refrigerant are counter flows, characterized in that the refrigerant comprises HFO-1132(E), R32, and R1234yf, wherein when the mass% of HFO-1132(E), R32, and R1234yf based on their sum in the refrigerant is respectively represented by x, y and z, coordinates (x,y,z) in a ternary composition diagram in which the sum of HFO-1132(E), R32, and R1234yf is 100 mass% are within the range of a figure surrounded by line segments ON, NU, and UO that connect the following 3 points: point O (22.6, 36.8, 40.6), point N (27.7, 18.2, 54.1), and point U (3.9, 36.7, 59.4), or on these line segments; the line segment ON is represented by coordinates (0.0072y 2 -0.6701y+37.512, y, -0.0072y 2 -0.3299y+62.488); the line segment NU is represented by coordinates (0.0083y 2 -1.7403y+56.635, y, -0.0083y 2 +0.7403y+43.365); and the line segment UO is a straight line, and the refrigerant comprises HFO-1132(E), R32, and R1234yf, wherein when the mass% of HFO-1132(E), R32, and R1234yf based on their sum in the refrigerant is respectively represented by x, y and z, coordinates (x,y,z) in a ternary composition diagram in which the sum of HFO-1132(E), R32, and R1234yf is 100 mass% are within the range of a figure surrounded by line segments ON, NU, and UO that connect the following 3 points: point O (22.6, 36.8, 40.6), point N (27.7, 18.2, 54.1), and point U (3.9, 36.7, 59.4), or on these line segments; point O (22.6, 36.8, 40.6), point N (27.7, 18.2, 54.1), and point U (3.9, 36.7, 59.4), or on these line segments; the line segment ON is represented by coordinates (0.0072y 2 -0.6701y+37.512, y, -0.0072y 2 -0.3299y+62.488); the line segment NU is represented by coordinates (0.0083y 2 -1.7403y+56.635, y, -0.0083y 2 +0.7403y+43.365); and the line segment UO is a straight line, and the refrigerant comprises HFO-1132(E), R32, and R1234yf in a total amount of 99.5 mass% or more based on the entire refrigerant. <EOS>