An air-conditioning apparatus, comprising an outdoor unit; an indoor unit; and a relay comprising a first relay unit and a second relay unit provided between the outdoor unit and the indoor unit to allow refrigerant to circulate between the first relay unit and the outdoor unit and between the second relay unit and the outdoor unit, and a heat medium circuit connecting the first relay unit and the second relay unit to the indoor unit to allow a heat medium to circulate through the heat medium circuit, wherein the second relay unit is installed above or on a top of the first relay unit; wherein the first relay unit includes a first pump configured to circulate the heat medium between the indoor unit and the first relay unit, the second relay unit includes a second pump configured to circulate the heat medium between the indoor unit and the second relay unit, characterized in that each of the first pump and the second pump has different horsepower, wherein the first pump has horsepower greater than does the second pump, wherein the first relay unit includes a first heat-medium heat exchanger that exchanges heat between the refrigerant and the heat medium, wherein the second relay unit includes a second heat-medium heat exchanger that exchanges heat between the refrigerant and the heat medium, wherein the relay comprises a first temperature sensor (43a, 45a) configured to detect a temperature of the refrigerant flowing out of the first heat-medium heat exchanger, a second temperature sensor (43b, 45b) configured to detect a temperature of the refrigerant flowing out of the second heat-medium heat exchanger, and a control unit configured to control a rotation frequency of the first pump, and the control unit includes a determination unit configured to determine whether a temperature difference between a value detected by the first temperature sensor (43a, 45a) and a value detected by the second temperature sensor (43b, 45b) is larger than or equal to a temperature threshold determined, and a pump control unit configured to decrease a rotation frequency of the first pump when the determination unit determines that the temperature difference is larger than or equal to the temperature threshold. an outdoor unit; an indoor unit; and a relay comprising a first relay unit and a second relay unit provided between the outdoor unit and the indoor unit to allow refrigerant to circulate between the first relay unit and the outdoor unit and between the second relay unit and the outdoor unit, and a heat medium circuit connecting the first relay unit and the second relay unit to the indoor unit to allow a heat medium to circulate through the heat medium circuit, wherein the second relay unit is installed above or on a top of the first relay unit; wherein the first relay unit includes a first pump configured to circulate the heat medium between the indoor unit and the first relay unit, the second relay unit includes a second pump configured to circulate the heat medium between the indoor unit and the second relay unit, characterized in that each of the first pump and the second pump has different horsepower, wherein the first pump has horsepower greater than does the second pump, wherein the first relay unit includes a first heat-medium heat exchanger that exchanges heat between the refrigerant and the heat medium, wherein the second relay unit includes a second heat-medium heat exchanger that exchanges heat between the refrigerant and the heat medium, wherein the relay comprises a first temperature sensor (43a, 45a) configured to detect a temperature of the refrigerant flowing out of the first heat-medium heat exchanger, a second temperature sensor (43b, 45b) configured to detect a temperature of the refrigerant flowing out of the second heat-medium heat exchanger, and a control unit configured to control a rotation frequency of the first pump, and the control unit includes a determination unit configured to determine whether a temperature difference between a value detected by the first temperature sensor (43a, 45a) and a value detected by the second temperature sensor (43b, 45b) is larger than or equal to a temperature threshold determined, and a pump control unit configured to decrease a rotation frequency of the first pump when the determination unit determines that the temperature difference is larger than or equal to the temperature threshold. a first temperature sensor (43a, 45a) configured to detect a temperature of the refrigerant flowing out of the first heat-medium heat exchanger, a second temperature sensor (43b, 45b) configured to detect a temperature of the refrigerant flowing out of the second heat-medium heat exchanger, and a control unit configured to control a rotation frequency of the first pump, and the control unit includes a determination unit configured to determine whether a temperature difference between a value detected by the first temperature sensor (43a, 45a) and a value detected by the second temperature sensor (43b, 45b) is larger than or equal to a temperature threshold determined, and a pump control unit configured to decrease a rotation frequency of the first pump when the determination unit determines that the temperature difference is larger than or equal to the temperature threshold.