A first DC/DC converter is provided between a rectifier for rectifying output of an electric generator driven by an engine, and a battery for supplying power to an in-vehicle load. An electric double layer capacitor and a second DC/DC converter for charge/discharge current control for the capacitor are provided between the rectifier and the first DC/DC converter. A control circuit sets a current target value which is a control target value for the second DC/DC converter, based on the voltage value of a battery bus, and when charging of the electric double layer capacitor is to be stopped based on a charge/discharge instruction signal, performs, before the charging is stopped, control of gradually attenuating the current target value for the second DC/DC converter, based on a voltage value VEDLC of the electric double layer capacitor.