An air-conditioning apparatus comprising: an outdoor unit including at least a compressor and an outdoor pipe (8a, 8b); an indoor unit including at least an indoor heat exchanger, an indoor fan, and an indoor pipe (9a, 9b); an extension pipe (10a, 10b) connecting the outdoor pipe and the indoor pipe to each other; a first temperature sensor disposed under a connection portion connecting the indoor heat exchanger and the indoor pipe to each other; and a control unit configured to determine whether a refrigerant having a higher specific gravity than indoor air is leaking from the connection portion, on the basis of a change in a temperature detected by the first temperature sensor, while the indoor fan is stopped, characterized in that: a first leaked refrigerant receiver is disposed under the connection portion and the first temperature sensor is disposed in the first leaked refrigerant receiver, the indoor heat exchanger includes a plurality of radiator plates and a plurality of heat-transfer pipes extending through the radiator plate, the indoor pipe (9a, 9b) comprises a gas-side indoor pipe and a liquid-side indoor pipe, a cylindrical header main pipe and a plurality of header branch pipes that is connected to the header main pipe are positioned between and connected to the gas-side indoor pipe and the indoor heat exchanger, a plurality of indoor refrigerant branch pipes are positioned between and connected to the liquid-side indoor pipe and the indoor heat exchanger, the connection portion comprises a brazed portion between the gas-side indoor pipe and the header main pipe, a brazed portion between the header main pipe and the header branch pipes, a brazed portion between the header branch pipes and a first end of the heat-transfer pipes, a brazed portion between a second end of the heat-transfer pipes and the indoor refrigerant branch pipes, and a brazed portion between the indoor refrigerant branch pipes and the liquid-side indoor pipe. an outdoor unit including at least a compressor and an outdoor pipe (8a, 8b); an indoor unit including at least an indoor heat exchanger, an indoor fan, and an indoor pipe (9a, 9b); an extension pipe (10a, 10b) connecting the outdoor pipe and the indoor pipe to each other; a first temperature sensor disposed under a connection portion connecting the indoor heat exchanger and the indoor pipe to each other; and a control unit configured to determine whether a refrigerant having a higher specific gravity than indoor air is leaking from the connection portion, on the basis of a change in a temperature detected by the first temperature sensor, while the indoor fan is stopped, characterized in that: a first leaked refrigerant receiver is disposed under the connection portion and the first temperature sensor is disposed in the first leaked refrigerant receiver, the indoor heat exchanger includes a plurality of radiator plates and a plurality of heat-transfer pipes extending through the radiator plate, the indoor pipe (9a, 9b) comprises a gas-side indoor pipe and a liquid-side indoor pipe, a cylindrical header main pipe and a plurality of header branch pipes that is connected to the header main pipe are positioned between and connected to the gas-side indoor pipe and the indoor heat exchanger, a plurality of indoor refrigerant branch pipes are positioned between and connected to the liquid-side indoor pipe and the indoor heat exchanger, the connection portion comprises a brazed portion between the gas-side indoor pipe and the header main pipe, a brazed portion between the header main pipe and the header branch pipes, a brazed portion between the header branch pipes and a first end of the heat-transfer pipes, a brazed portion between a second end of the heat-transfer pipes and the indoor refrigerant branch pipes, and a brazed portion between the indoor refrigerant branch pipes and the liquid-side indoor pipe. a first leaked refrigerant receiver is disposed under the connection portion and the first temperature sensor is disposed in the first leaked refrigerant receiver, the indoor heat exchanger includes a plurality of radiator plates and a plurality of heat-transfer pipes extending through the radiator plate, the indoor pipe (9a, 9b) comprises a gas-side indoor pipe and a liquid-side indoor pipe, a cylindrical header main pipe and a plurality of header branch pipes that is connected to the header main pipe are positioned between and connected to the gas-side indoor pipe and the indoor heat exchanger, a plurality of indoor refrigerant branch pipes are positioned between and connected to the liquid-side indoor pipe and the indoor heat exchanger, the connection portion comprises a brazed portion between the gas-side indoor pipe and the header main pipe, a brazed portion between the header main pipe and the header branch pipes, a brazed portion between the header branch pipes and a first end of the heat-transfer pipes, a brazed portion between a second end of the heat-transfer pipes and the indoor refrigerant branch pipes, and a brazed portion between the indoor refrigerant branch pipes and the liquid-side indoor pipe.