An air conditioning apparatus (100, 100a), wherein a compressor including a compression chamber inside a hermetically sealed container thereof, a first heat exchanger, at least one first expansion device, and at least one second heat exchanger are connected by refrigerant pipes to form a circuit constituting a refrigeration cycle, the air-conditioning apparatus comprising an accumulator for accumulating excess refrigerant provided on a channel on a suction side of the compressor, a suction injection pipe for externally introducing refrigerant in a liquid or a two-phase state into a channel between the compressor and the accumulator, and a second expansion device provided to the suction injection pipe, the air conditioning apparatus comprising a third expansion device that generates a medium pressure smaller than the high pressure and larger than the low pressure during the heating operation in a channel of refrigerant from the at least one second heat exchanger to the first heat exchanger during the heating operation, and wherein a channel on an upstream side of the third expansion device and a channel on an upstream side of the second expansion device are configured to be connected during the heating operation, and the medium pressure refrigerant generated by the third expansion device, during the heating operation, is introduced on a suction side of the compressor via the second expansion device and the suction injection pipe, characterized in that the air conditioning apparatus further comprises a first refrigerant flow switching device, a first branching unit that is configured to cause refrigerant to branch from a refrigerant channel in a case where refrigerant is flowing from the first heat exchanger to the at least one first expansion device, a second branching unit that is configured to divert refrigerant from a refrigerant channel in a case where refrigerant is flowing from the at least one first expansion device to the first heat exchanger; a branch pipe that is configured to connect the first branching unit and the second branching unit, with the suction injection pipe connected thereto, a first conducting device installed between the first branching unit and a joint between the branch pipe and the suction injection pipe, a second conducting device installed between the second branching unit and the joint, and a detection device that is suitable to detect a pressure or a temperature of the medium pressure refrigerant, wherein the air-conditioning apparatus comprises a controller that is configured to perform a heating operation, in which at least low pressure refrigerant flows into the first heat exchanger to cause it to serve as an evaporator, and high pressure refrigerant flows into some or all of the at least one second heat exchanger to cause them to serve as at least one condenser, wherein the controller is configured to i) control the second expansion device such that either a refrigerant discharge temperature on a discharge side of the compressor, or a refrigerant discharge superheat degree computed from the refrigerant discharge temperature and a pressure on a discharge side of the compressor, approaches a target value, or is within a target range, and ii) control a flow rate of refrigerant flowing to a suction side of the compressor via the second expansion device and the suction injection pipe; and iii) control the third expansion device such that a detected pressure of the detection device or a saturation pressure of a detected temperature of the detection device, or alternatively, a detected temperature of the detection device or a saturation temperature of the detected pressure of the detection device, approaches a target value, or is within a target range. i) control the second expansion device such that either a refrigerant discharge temperature on a discharge side of the compressor, or a refrigerant discharge superheat degree computed from the refrigerant discharge temperature and a pressure on a discharge side of the compressor, approaches a target value, or is within a target range, and ii) control a flow rate of refrigerant flowing to a suction side of the compressor via the second expansion device and the suction injection pipe; and iii) control the third expansion device such that a detected pressure of the detection device or a saturation pressure of a detected temperature of the detection device, or alternatively, a detected temperature of the detection device or a saturation temperature of the detected pressure of the detection device, approaches a target value, or is within a target range.