In the present invention, when a motor generator (7) connected to an engine (8) is operated as a generator and collects the kinetic energy of a vehicle as electrical power, during the initial period of charging a battery pack (1), a program timer (4a) closes all switch circuits (23-26), the regenerated power from the motor generator (7) is used in the charging of a capacitor (14) and in consumption at resistors (15, 16), and the charging current at the start of charging flowing to the battery pack (1) is suppressed. Furthermore, with the switch circuit (23) remaining closed, the switch circuits (26) and (25) are sequentially opened, and the switch circuit (24) for the capacitor (14) is opened last, thereby gradually reducing the rate of suppression of the charging current to the battery pack (1) and increasing the charging current when not performing suppression, thereby lengthening the cycle lifetime of the battery pack (1) charged by the generator that uses kinetic energy to regenerate regenerated power.