An ozonizer was devised in which a lead wire, as the electrode, is passed through the center of an insulator tube, such as glass and synthetic resin tubes, this central electrode is wound with a spiralling insulator so as to make the space between the central electrode and inner wall of the tube uniform. Amount of ozone produced per unit time was compared between this ozonizer and the Siemens tube. It was thereby found that the new apparatus is 1/10 of the Siemens tube in total volume, lower in discharge voltage, about five times greater in electric power per unit discharge area, and the rate is 70% to around 55% in the Siemens tube. Moreover, this new tube is easier to make and a long one of 1-2m. can be made, so that ozone of low to high concentrations can be produced freely.