PURPOSE: To reduce the size and the cost of an equipment by connecting a plurality of parallel connections of constant voltage circuits which output a prescribed voltage in accordance with a secondary battery to be charged with a constant current charging power supply in series.

CONSTITUTION: A constant voltage circuit 2 is connected in parallel with a secondary battery 1 to be charged, for example, a lithium secondary battery. The circuit 2 outputs a prescribed voltage in accordance with the battery 1. The circuit 2 has a positive-side current terminal 3 and voltage terminal 4 and a negative-side voltage terminal 5 and current terminal 6. The positive-side terminals are connected to the positive side of the battery 1 and the negative-side terminals are connected to the negative side of it. A plurality of parallel combinations of the battery 1 and the circuit 2 are connected in series with a constant current power supply 7. A commercial power supply is connected to the power supply 7 through a timer 8 which terminates the charging of the battery 1. While the terminal voltage is the same as a set value of the circuit 2 or below, all the output current of the power supply 7 flows into the battery 1. When the terminal voltage reaches the set level, charging is performed with voltage being controlled at the set level. By this method, many batteries can be charged rapidly by means of a small and low-cost equipment.