PURPOSE: To facilitate mounting of a generator even onto a monocoque body vehicle having integral structure of body and frame or a vehicle on which a power take-out device cannot be mounted by simplifying the control circuit for an electric generator.

CONSTITUTION: A detection voltage of an AC three-phase generator 2 coupled with a travel engine 1 is converted through a converter 3 into a DC voltage which is then smoothed through a voltage waveform smoothing circuit 4. Thus smoothed DC voltage is then inverted through an inverter 5 into an AC voltage which is then smoothed through an AC filter circuit 6. A control circuit 8 detects a signal fed from the AC filter circuit 6 and controls the base voltage of a switching transistor in the inverter 5 based on thus detected signal. According to the arrangement, overall constitution can be simplified, overall size can be reduced and the number of component can be decreased.