Abstract: The rotor damping and control power value can be made arbitrary by controlling a cyclic pitch control mechanism with a signal proportional to the angular acceleration of the attitude angle .theta., a signal proportional to the angular velocity of the attitude angle .theta., and a correction signal based upon the difference between the attitude angle .theta. and assumed attitude angle .theta..sub.0, plus the cyclic pitch control input .PSI. applied to a cyclic pitch lever of a pilot. Thus, the rotor damping and control power are brought to their optimum values in response to the actual flight conditions of a helicopter for ideal operability, resulting in both high stability and operability, and, for example, fully automatically controlled hovering can be accomplished without producing any vibration in the attitude angle control response.