PURPOSE: To realize the reduction of a charging time by a method wherein all battery groups are charged in series with a constant current until battery voltages reach a limit voltage and, after that, the individual groups are successively charged with a constant current by switching the charging circuits.

CONSTITUTION: When respective groups 1A and 1B of batteries A and B are charged, respective relay switches 2A, 2B and 2C are turned to the contacts (a), (b) and (b). When the batteries A of the group 1A only are charged, the respective relay switches 2A, 2B and 2C are turned to the contacts (a), (a) and (a) and, when the batteries B of the group B only are charged, the respective relay switches 2A, 2B and 2C are turned to the contacts (b), (a) and (b). The relay switches 2A, 2B and 2C are controlled to be turned by a charge controller 4. The charge controller 4 turns the relay switches 2A, 2B and 2C so as to have the battery groups 1A and 1B in series for charging until the battery voltage applied to a charge power supply 3 does not reach a limit voltage. After the battery voltage reaches the limit voltage, the relay switches 2A, 2B and 2C are controlled to be turned so as to charge the battery groups 1A and 1B alternately and individually. With this constitution, the charging time can be reduced.