PURPOSE: To effectively balance in an irregular fluctuation by providing an automatic rotation controller for automatically controlling a rotary angle of a steering wing as a function of a simultaneous pitch angle of a single rotor and a forward speed of a helicopter.

CONSTITUTION: A simultaneous pitch angle DTORP given by a position sensor 15 corresponding to a control lever 16 and a forward speed V given by a sensor 17 are given to a computer 18, and a rotary value δ to be operated at a rudder 14 is given. The value δ is operated at an actuator 19 for controlling rotation of the rubber 14 around an axial center X-X to regulate a pitch of blade 12 of an anti-torque rotary blade 10 and to set a thrust YRA to zero. The computer 18 has a table for bringing measured set of the angle DTORPi and the speed Vi corresponding to a suitable value δi, and the value δi corresponding in the table is checked and operated at the actuator 19.