PURPOSE: To charge a battery positively even when load is connected simultaneously by mounting a changeable resistance circuit so that the quantity of conduction is increased when both load and the battery are connected.

CONSTITUTION: In a charging circuit often supplying even load 5 with electric power at the same time as a battery 4 is charged, resistors RAC, RE are set up into a circuit for a changeover switch 6 for supplying the load 5 with electric power. A resistance value at a time when even the load 5 is supplied with electric power is made smaller than a resistance value at a time when the battery 4 is charged only, thus increasing the quantity of conduction. Accordingly, charging currents to the battery 4 can be ensured sufficiently even when the load 5 is supplied with electric power, thus positively charging it.