To improve torque characteristic at low rotation and reduce the size and weight of an electric rotating machine by arranging it so that when a rotary shaft, a yoke provided with permanent magnets and coupled with the rotary shaft, and a stator encircling the yoke are provided, making the magnetic characteristics of the yoke variable, depending on the rotation of the rotary shaft, and making the inertial mass of the rotary shaft relatively small.

A centrifugal governor 9 provided with a moving member 16, which moves towards a yoke 8 as the number of rotations of the rotary shaft 6 is increased, is installed on the rotary shaft 6. An auxiliary yoke 21, which reduces the magnetic reluctance of the yoke 8 as the moving member 16 moves towards the yoke 8 and increases the magnetic reluctance of the yoke 8, as the moving member 16 which is moved away from the yoke 8 is coupled with the moving member 16.