To restrain the increase in the weight of an airframe.

This auxiliary power unit 1 is provided with an air intake 2, a nozzle unit 3, an exhaust nozzle 4, a turbine 5, a bevel gear 6 and a gearbox 7. The air intake 2 is used to intake high-speed air and the nozzle unit 3 is used to increase the flow velocity of the air. The exhaust nozzle 4 is placed at the latter part of the nozzle unit 3 and the turbine 5 is placed in the exhaust nozzle 4. The bevel gear 6 bends the direction of a revolving shaft at right angle. The gearbox 7 for adjusting the number of revolutions is journalled to a hydraulic pump 9. The turbine 5 rotates when high-speed air is taken in the air intake 2. The rotation of the turbine 5 is transmitted to the gearbox 7 through the bevel gear 6. The change of the speed is made in the gearbox 7. The hydraulic pump 9 is driven by the revolving power from the gearbox 7.