To improve cooling capability during parking by driving an air cycle machine with the engine bleed air or an electric motor.

The shaft S of an air cycle machine 3 can be driven by an electric motor M. When an engine 1 is rotated at a high speed and sufficient bleed air is available, the bleed air is fed to a turbine T as fresh air to rotatively drive the turbine T, the rotating power is transmitted to a compressor C via the shaft S, and the whole air cycle machine 3 is operated. When the bleed air is not sufficient during parking, the air cycle machine 3 is driven by the electric motor M. Even in the idle state of the engine 1, the air cycle machine 3 is rotated at a high speed to compress and introduce sufficient outside air, and cooling in an aircraft can be effectively made.