PURPOSE: To suppress noise, occurring upon turn ON of an exciting coil, through a simple circuitry and to reduce provability of failure by providing a generator incorporating an exciting coil and an armature coil for generating an electromotive force corresponding to the variation of field and a semiconductor element for supplying and interrupting current to/from the exciting coil.

CONSTITUTION: When the battery voltage exceeds a regulation voltage, a comparator 14 produces a Hi output signal. Consequently, output of an inverter 25 in a charge pump circuit 11 is inverted to (to) and a transistor 24 is turned OFF thus interrupting power supply to the gate. On the other hand, a transistor 34 in a gate discharge circuit 12 receives Hi output from the comparator 14 and turned ON thus blocking the current 12 of a constant current circuit 36 from being fed to a transistor 33. Furthermore, a transistor 35 is turned OFF and current 13 is fed from a constant current circuit 37 to the transistor 33. Consequently, the current 13 of the constant current circuit 37 is fed to a transistor 32 thus discharging the gate thereof. As a result, a semiconductor element 8 is turned OFF and the exciting current of an exciting coil 4 decreases thus reducing the power to be produced by a generator 3.