PURPOSE: To stabilize an ozone generating quantity of an ozone generator by arranging an amplitude restricting means to restrict voltage amplitude of commercial electric power supply, and making voltage impressed on a high voltage generator constant to a change in electric power supply voltage.

CONSTITUTION: Sine wave voltage of a plus half period of commercial electric power supply is impressed on terminals 2 and 3 of an amplitude restricting means 10, and when the voltage is increased and voltage between terminals 18a and 18c of a three- terminal constant voltage element 18 exceeds a prescribed value, constant voltage is generated between terminals 18b and 18c. When the voltage between the terminals 18b and 18c of the element 18 becomes constant voltage, an electric current of resistors 14 and 15 and a volume 16 becomes equal to an electric current of a resistor 17, and voltage between terminals 4 and 5 becomes constant, and the voltage of the plus half period of the commercial electric power supply is restricted in amplitude. Since a high voltage generator 30 is driven by this voltage, even if the voltage of the electric power supply is changed, amplitude of high frequency/high voltage generated in a secondary side coil 34B of a high frequency transformer 14 becomes also a constant value. Thereby, an ozone quantity generated by a corona discharger 45 becomes constant.