An air-conditioning apparatus having a refrigeration cycle in which a compressor, a refrigerant flow switching device, a heat source side heat exchanger, a use side expansion device, and a use side heat exchanger are connected to one another using a refrigerant pipe, the air-conditioning apparatus comprising: an injection pipe having one side connected to an injection port of the compressor, and the other side connected to the refrigerant pipe between the use side expansion device and the heat source side heat exchanger, the injection pipe being configured to inject a refrigerant during a compression operation of the compressor; a refrigerant heat exchanger configured to exchange heat between the refrigerant, upon flowing through the refrigerant pipe in the refrigeration cycle, and the refrigerant, upon flowing through the injection pipe; an accumulator having one side connected to a suction side of the compressor, and the other side connected to the refrigerant flow switching device, the accumulator being configured to store a liquid refrigerant; an additional connecting pipe having one side connected to the suction side of the compressor, and the other side connected to a bottom of the accumulator; an opening and closing device provided to the connecting pipe and capable of switching between opening and closing of a passage in the connecting pipe; and a controller configured to, in a case of a heating operation in which the use side heat exchanger functions as a condenser when outside air has a predetermined low temperature, execute a low-outside-air-temperature heating operation start mode in which, while the refrigerant, as discharged from the compressor, flows into the use side heat exchanger, the refrigerant is supplied to the injection port of the compressor via the injection pipe and a part of the refrigerant, as accumulated in the accumulator, is supplied to the compressor via the connecting pipe, and thereafter to execute a low-outside-air-temperature heating operation mode in which the refrigerant, as discharged from the compressor, is supplied to the injection port of the compressor via the injection pipe while flowing into the use side heat exchanger. an injection pipe having one side connected to an injection port of the compressor, and the other side connected to the refrigerant pipe between the use side expansion device and the heat source side heat exchanger, the injection pipe being configured to inject a refrigerant during a compression operation of the compressor; a refrigerant heat exchanger configured to exchange heat between the refrigerant, upon flowing through the refrigerant pipe in the refrigeration cycle, and the refrigerant, upon flowing through the injection pipe; an accumulator having one side connected to a suction side of the compressor, and the other side connected to the refrigerant flow switching device, the accumulator being configured to store a liquid refrigerant; an additional connecting pipe having one side connected to the suction side of the compressor, and the other side connected to a bottom of the accumulator; an opening and closing device provided to the connecting pipe and capable of switching between opening and closing of a passage in the connecting pipe; and a controller configured to, in a case of a heating operation in which the use side heat exchanger functions as a condenser when outside air has a predetermined low temperature, execute a low-outside-air-temperature heating operation start mode in which, while the refrigerant, as discharged from the compressor, flows into the use side heat exchanger, the refrigerant is supplied to the injection port of the compressor via the injection pipe and a part of the refrigerant, as accumulated in the accumulator, is supplied to the compressor via the connecting pipe, and thereafter to execute a low-outside-air-temperature heating operation mode in which the refrigerant, as discharged from the compressor, is supplied to the injection port of the compressor via the injection pipe while flowing into the use side heat exchanger.