PURPOSE: To provide an ozonizer capable of increasing the output of ozone without increasing the power consumption or enlarging its scale.

CONSTITUTION: This ozonizer consists of a plate insulator 2 provided with a wire electrode 3 on its front 2a and a sheet electrode 4 on the rear 2b and a discharge chamber 9 formed on the front side of the insulator, the wire electrode and sheet electrode are connected respectively to an AC high-frequency power source 8 to generate a silent surface discharge, and ozone is generated. A gas diffuser 13 is furnished close to the inlet 11 and/or outlet 12 for a gas treated in the discharge chamber 9, and the treated gas is uniformly diffused in the discharge chamber and allowed to flow uniformly.