Abstract: There is provided an ozonizer with an ozonizer element which has a columnar shaft body, a positive electrode of a platinum net plate which is fitted around an outer surface of the columnar shaft body, an ion exchange membrane fitted around the positive electrode, and a negative electrode of a metal net fitted around the ion exchange membrane. The positive electrode is intermittently wound around the columnar shaft body with a predetermined axial interval or otherwise an intermittent insulator is provided in an axial direction between the positive electrode and the negative electrode. The ozonizer has a tubular passage for permitting water to flow therethrough and housing therein the ozonizer element such that an axis of the ozonizer lies in the flowing direction of the water. Further the ozonizer has a device for applying DC voltage between the positive electrode and the negative electrode so that a discharge portion and non-discharge portion are alternately located in the water flowing direction.