Method and apparatus for quickly and efficiently charging an electric double layer capacitor. The capacitor is charged by a constant-current power supply which is preferably a current controlled output type switching power supply. To cause the voltage across the terminals of the capacitor to reach its working voltage in a short time, the capacitor is overcharged for a short time. Where the capacitor is charged with a solar battery, a constant-current output type switching regulator is interposed between the solar battery and the capacitor.