A charging device includes a case that surrounds a charging unit and has plural ventilating sections, a gas separating unit that varies a component ratio of the air near an opposed portion of a photosensitive member and the charging unit, and a gas electrolyzing unit that electrolyzes moisture of the area near the opposed portion. The gas separating unit has a nitrogen enriching unit that includes a nitrogen enriching film set in a ventilating section and a pressurizing chamber for forming a pressure difference between the inside and the outside of the case and supplies a nitrogen enriched air to the inside of the case or an oxygen enriching unit that includes an oxygen enriching film set in another ventilating section and a depressurizing chamber for forming a pressure difference between the inside and the outside of the case and exhausts an oxygen enriched air to the outside of the case.