NOVELTY - The ozonizer operation method comprises tightly adhering an anode (2) for ozone generation in the ozonizer to one face of the lateral faces of a solid polymer electrolyte membrane (1) comprising a cation exchange membrane, in front of which an anode compartment (6) is configured and then tightly adhering a cathode (4) for hydrogen generation in the ozonizer to the other face of the lateral faces, in front of which a cathode compartment (7) is configured, where ozone gas is generated at the anode in the anode compartment and hydrogen gas is generated at the cathode in the cathode compartment.    USE - The method is useful for operating an ozonizer.    ADVANTAGE - The operation method improves ozone gas purity, and achieves safe and continuous operation for a long period of time.    DETAILED DESCRIPTION - The ozonizer operation method comprises tightly adhering an anode (2) for ozone generation in the ozonizer to one face of the lateral faces of a solid polymer electrolyte membrane (1) comprising a cation exchange membrane, in front of which an anode compartment (6) is configured and then tightly adhering a cathode (4) for hydrogen generation in the ozonizer to the other face of the lateral faces, in front of which a cathode compartment (7) is configured, where ozone gas is generated at the anode in the anode compartment and hydrogen gas is generated at the cathode in the cathode compartment during normal operation of the ozonizer, and applying the cathode as a reversible electrode with two functions as a gas generation electrode and a gas electrode. Only when the ozonizer is stopped and the operation is switched to protective current operation during which minute electric current is supplied to protect the anode, the electrolyte and hydrogen gas are all drained out and then oxygen-containing gas is supplied to the cathode compartment to make the cathode function as a gas electrode to perform oxygen reduction reaction, and deionized water, air or inert gas is supplied into the cathode compartment and the oxygen-containing gas is supplied to the cathode compartment after electrolyte and hydrogen gas in the cathode compartment are all replaced with deionized water, air or inert gas. The cathode is formed by an electroconductive porous structure comprising platinum or platinum-supported carbon particles dispersed in fluororesin-containing resin. The anode is formed by an electroconductive porous structure comprising a porous metal plate or a metal fiber sintered object with lead dioxide-contained anode catalyst on its surface. An INDEPENDENT CLAIM is included for an ozonizer to implement the operation method.    DESCRIPTION OF DRAWING(S) - The diagram shows an overall view of an operation method of an ozonizer and an electrolytic cell used for the ozonizer.    Solid polymer electrolyte membrane (1)    Anode (2)    Cathode (4)    Anode compartment (6)    Cathode compartment. (7)