An electric double layer capacitor which is usable at a high voltage without causing an irreversible current. Both a polarized positive electrode 14 and a polarized negative electrode 16 are made of the same constituents. However, a ratio of an amount of constituents of the polarized positive electrode 14 differs from that of the polarized negative electrode 16. A ratio of a capacitance of the polarized positive electrode to a capacitance of the polarized negative electrode is controlled such that the polarized positive electrode and the polarized negative electrode simultaneously reach respective potentials where the irreversible current is caused. According to this invention there is an advantage that it is possible to increase a voltage applied to the electric double layer capacitor.