To charge efficiently an electric double layer capacitor in a short time.

Electric energy is beforehand stored in the electric double layer capacitor C1 for a master. When a switch SW1 is switched to conduction, a serial resonance circuit is formed of the electric double layer capacitor C1 for the master, an electric double layer capacitor C2 for a slave and a coil L1. Accordingly, the voltage of the electric double layer capacitor C2 for the slave is oscillated. The switch SW1 of a continuity state is switched to non-conduction at the timing t1 in which the oscillating voltage of the electric double layer capacitor C2 for the slave serves as substantial maximum, and the charging of the electric double layer capacitor C2 for the slave is completed.