An ozone generator includes a transformer, a direct current power supply unit connected to a primary side of the transformer, a reactor connected to a secondary side of the transformer, a semiconductor switch connected between at least one end of a primary winding of the transformer and the direct current power supply unit, and a control circuit for implementing ON-OFF control of the semiconductor switch to thereby apply alternating current voltage to the reactor. The control circuit implements control of a frequency of the alternating current voltage applied to the reactor, so as to minimize electric signal on the primary side of the transformer.