To provide an air conditioner capable of keeping a predetermined cooling capability even if an engine extraction gas is reduced.

Cooling air B4 is generated by an air cycle system 1 constituted of an air cycle machine 30 having a two-stage turbine as a main element. Recirculation air B5 is cooled by a vapor cycle 2 composed of a compressor 24 having an electric motor 25, a condenser 21 for condensing gaseous refrigerant G, an expansion valve 22 for expanding liquid refrigerant L and changing it into low pressure refrigerant and an evaporator 23 for evaporating the liquid refrigerant L and cooling it. The cooling air B4 and recirculation air B5 are mixed to each other and supplied to a device pressurizing chamber R. A heat exchanger 14 is provided for recovering energy of the heat energy of the liquid refrigerant L outputted from the condenser 21 to the low pressure air B3 discharged from a first-stage turbine 32 of the air-cycle system 1.

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