PURPOSE: To increase an output from a generator by boosting and rectifying one part of an output from an armature coil and supplying an exciting coil with one part of the output.

CONSTITUTION: A boosting and rectifying circuit 5 is connected in parallel with a main rectifier circuit 2 to a three-phase armature coil 1. The circuit 5 consists of auxiliary diodes 6a∼6c and capacitors 7a, 7b, 8a, 8b, 9a, 9b, and constitutes a voltage doulbing rectifier circuit. An output from the boosting and rectifying circuit 5 is connected to an exciting coil 10. Another side of the exciting coil 10 is connected to a voltage regulator 11 for controlling exciting currents and adjusting output voltage from a generator at fixed voltage. Accordingly, exciting currents can be increased, thus elevating an output.