PURPOSE: To facilitate initial charging with a built-in battery inside.

CONSTITUTION: A main circuit to which the output of an AC generator 20 whose prime mover is an engine 10 is inputted and a control circuit 50 which controls the main circuit are provided. The main circuit has a converter circuit 31 which rectifies and converts the output of the AC generator into a DC output, a smoothing capacitor 32 which smoothes the DC output, an inverter circuit 33 which converts the voltage of the smoothing capacitor 32 into an AC voltage and an output circuit which smoothes the single phase output of the inverter circuit 33 with an LC filter and transmits the smoothed output to apparatus output terminals T01 and T02. Further, the converter circuit 31 and the inverter circuit 33 are composed of bridge circuits of transistors including reverse-parallel diodes and the charging power of a built-in battery 41 is received through the apparatus output terminals T01 and T02.