PURPOSE: To share a charger for a main battery and a battery for an auxiliary engine by stepping down the DC voltage being rectified with a third rectifier circuit, based on the second AC converted from the DC power of a main battery, and outputting it to the battery for an auxiliary engine.

CONSTITUTION: A reactor L10 and a power factor improving circuit 3 consisting of a diode 3a for rectification and a switching transistor 3a and a switching transistor TX1 are connected between the output terminals of a first rectifying circuit 2. TX1 improves the power factor, and steps up the output voltage, and smooths it, and drives an inverter 5, being opened and closed with the signal X1 of a control circuit 4. The transistors T1-T4 of the inverter 5 outputs a first high frequency current, and adds it to the primary winding a of the transistor TR3, being opened and closed with signals S1-S4. The secondary winding b is connected to the rectifier circuit 6 so as to charge the main battery B1. An inverter 7 opens and closes the DC of the main battery B1 with control signals G1-G4, and generates a second high frequency AC, and outputs it to winding b. The high-frequency current induced in winding a is added to a voltage adjusting circuit 9, and it is charged in a battery B2 for an auxiliary engine.