To provide a method for amplifying an output torque by an electric torque motor of a system, such as vehicle electronic throttle control system or the like.

When a throttle plate T of an electronic throttle system and its periphery are frozen, the output torque of a torque motor 10 coupled with a throttle plate T is amplified up to the torque for adequately overcoming freezing or other troubles from the ordinary operation torque. One torque is given to a rotor 38 of the torque motor 10 to twist an output shaft 34 coupled with the fixed throttle plate T. Thereafter, the torque is inverted, and this inverted torque is then given to the rotor 38. Such inversion of torque is continuously repeated for the number of selected vibrations which is equal to the fixed number of vibration of a mechanical system, using the throttle plate T and torque motor 10 as the parts in order to generate the resonance condition. As a result, the torque to be given to the rotor 38 is amplified, up to the level to adequately overcome freezing and other troubles.