To shorten a charging time by charging a plurality of batteries simultaneously with charging power of one battery without changing the weight and external dimensions of a charging device.

Based on the charging current of a battery 71 obtained through a detecting resistor 61, an OP-amp 521 and an A/D converter, an operating means 4 calculates the charging current of a battery 72 in such a way as to keep electric energy constant. The charging current so calculated limits the charging current of the battery 72 by a pulse width modulating means 3, and this pulse width modulating means 3 turns on a switching device 22 to charge the battery. Then, the operating means 4 always detects the decrease of the charging current of the battery 71, so that, according to this detected result, the pulse width modulating means 3 increases the charging current of the battery 72 via the switching device 22.