PURPOSE: To realize highly efficient power generation and to considerably contribute to high performance high output power generation by a constitution wherein a stator coil for exciting a field coil, a rectifier and a regulator are provided and a divided exciting output voltage is applied on the field coil.

CONSTITUTION: As the rotational speed of engine increases from a standard rotational speed, voltage generated from a stator coil 1 increases gradually thus increasing the voltage at point B. Consequently, the voltage divided by voltage detecting resistors 8h, 8i and applied on the base of a comparing/ amplifying transistor 8f increases and the potential difference from the reference voltage of a Zener diode 8g enlarges thus increasing the base current of the comparing/amplifying transistor 8f correspondingly. As a result, inner resistance decreases and the collector current increases and thereby the voltage drop across resistors 8a, 8b increases thus lowering the potential at point A.