PURPOSE: To prevent deformation of a lower power gear box by a flying load, and reduce noise and vibration largely by setting the flying load of blades, etc., to get into an installation mount directly through an upper flying load gear box instead of getting into the lower power box.

CONSTITUTION: A flying load W of blades 1 and a rotor head 2 is transmitted to an upper flying load gear box 3 to be transmitted to an installation mount 4, while a rotation torque is set to be transmitted from a lower power gear box 6 through a universal joint 5. An output from an engine 7 gets into the lower power gear box 6, where necessary speed reduction and rotary shaft direction conversion are performed. Self-weight, inverse rotation torque, and gear mesh vibration are set to go through a vibration absorbing damper 8 to the installation mount 4. Vibration and noise given to an aircraft body can thus be reduced, and the fatigue life of an aircraft structure can be improved.