An outdoor unit includes at least a compressor, a gas-liquid separator, and an outdoor heat exchanger of a refrigerant circuit, the refrigerant circuit being formed by connecting, by pipes, the compressor, a condenser, a pressure reducing device, the gas-liquid separator, and the outdoor heat exchanger that acts as an evaporator including at least a plurality of heat transfer tubes and an inlet header that distributes incoming refrigerant to the heat transfer tubes. The outdoor unit further includes a gas-liquid-separator bypass pipe, a gas-liquid-separator-side flow control valve, a header bypass pipe, a header-side flow control valve, and a determination device.