To supply air for a pre-load into an aircraft to cool, heat, and ventilate the inside of the aircraft and increasing cooling capability in the aircraft during parking effectively.

This air conditioner for the aircraft is mainly composed of an air cycle machine constituted by connecting a turbine with a compressor by a single shaft and is constituted to drive the air cycle machine by first exhaust air from a pre-load chamber and drive it also by an electric motor other than the exhaust air. This air conditioner is provided with a recirculation circuit for mixing the second exhaust air taken out of the pre-load chamber independently from the first exhaust air with ram air compressed by the air cycle machine, cooling the mixed air by a vapor cycle system, and introducing it into the pre-load chamber again.