An air conditioning apparatus comprising a refrigerant circuit having a compressor, an outdoor heat exchanger, indoor heat exchangers (42a, 42b), and a heat storage heat exchanger for performing heat exchange between a refrigerant and a heat storage medium, the air conditioning apparatus being configured to perform a heat storage operation for storing heat in the heat storage medium by causing the heat storage heat exchanger to function as a heat radiator of the refrigerant, and, during a defrosting operation for defrosting the outdoor heat exchanger by causing the outdoor heat exchanger to function as a heat radiator of the refrigerant, simultaneously perform a heat-storage-utilizing operation for radiating heat from the heat storage medium by causing the heat storage heat exchanger to function as an evaporator of the refrigerant and an air-warming operation for causing the indoor heat exchangers to function as heat radiators of the refrigerant; wherein the refrigerant circuit also has indoor expansion valves (41a, 41b) for varying the flow rate of the refrigerant flowing through the indoor heat exchangers, and an outdoor expansion valve for varying the flow rate of the refrigerant flowing through the outdoor heat exchanger; the indoor heat exchangers and the indoor expansion valves are provided to indoor units (4a, 4b); and the outdoor heat exchanger and the outdoor expansion valve are provided to an outdoor unit; characterized in that the indoor units have indoor-side control parts (48a, 48b) for deciding the opening degrees of the indoor expansion valves when only the air-warming operation is performed; and the outdoor unit has an outdoor-side control part for deciding the opening degree of the outdoor expansion valve when only the air-warming operation is performed and deciding the opening degrees of the indoor expansion valves and the opening degree of the outdoor expansion valve when the air-warming operation is performed during the defrosting operation accompanying the heat-storage-utilizing operation; when the air-warming operation is performed during the defrosting operation accompanying the heat-storage-utilizing operation, the opening degrees of the indoor expansion valves (41a, 41b) are decided by the outdoor-side control part on the basis of the correlation between the condensation temperature of the refrigerant in the refrigerant circuit and the indoor temperatures of the spaces being air-conditioned by the indoor units (4a, 4b), until a first defrosting time (taj) elapses from the start of the defrosting operation. the refrigerant circuit also has indoor expansion valves (41a, 41b) for varying the flow rate of the refrigerant flowing through the indoor heat exchangers, and an outdoor expansion valve for varying the flow rate of the refrigerant flowing through the outdoor heat exchanger; the indoor heat exchangers and the indoor expansion valves are provided to indoor units (4a, 4b); and the outdoor heat exchanger and the outdoor expansion valve are provided to an outdoor unit; characterized in that the indoor units have indoor-side control parts (48a, 48b) for deciding the opening degrees of the indoor expansion valves when only the air-warming operation is performed; and the outdoor unit has an outdoor-side control part for deciding the opening degree of the outdoor expansion valve when only the air-warming operation is performed and deciding the opening degrees of the indoor expansion valves and the opening degree of the outdoor expansion valve when the air-warming operation is performed during the defrosting operation accompanying the heat-storage-utilizing operation; when the air-warming operation is performed during the defrosting operation accompanying the heat-storage-utilizing operation, the opening degrees of the indoor expansion valves (41a, 41b) are decided by the outdoor-side control part on the basis of the correlation between the condensation temperature of the refrigerant in the refrigerant circuit and the indoor temperatures of the spaces being air-conditioned by the indoor units (4a, 4b), until a first defrosting time (taj) elapses from the start of the defrosting operation.