PURPOSE: To provide an unmanned helicopter having improved controllability.

CONSTITUTION: An unmanned helicopter has an engine 6 serving as a power source, a rotor 4 driven by the engine 6 to generate propelling power, and power transmitting means 9 for decelerating the rotation of the engine 6 at a fixed deceleration ratio at which the rotor 4 attains normal rotating speed when engine rotating speed N1 is higher than rotating speed N0 at the time of maximum output of the engine 6 to transmit the rotation to the rotor 4.