The present invention provides a polarized electrode 12 containing mixed activated carbon composed of at least two activated carbons with different specific surface areas, and the specific surface area of the mixed activated carbon is not less than 900 m2/g and less than 1900 m2/g. By setting the specific surface area of the mixed activated carbon to less than 1900 m2/g, the resistance reduction ratio of the polarized electrode 12 rapidly increases.