In an electric double layer capacitor including two plate-like polarizable electrodes stacked in layers via a separator and constituted by housing these in an outer packaging member, a contact area between a first polarizable electrode and the separator is different from a contact area between a second polarizable electrode and the separator, and the polarizable electrode with a smaller contact area is formed thicker than the polarizable electrode with a larger contact area. In addition, it is preferable that the first polarizable electrode and the second polarizable electrode have a generally equal volume.