To provide an ozone gas generating apparatus supplying ozone gas with good response to variation in demand of ozone gas.

The ozone gas generating apparatus includes: a vaporizer 35 which stores therein liquid ozone introduced from a separation tank 34 and vaporizes the liquid ozone to generate ozone gas; a heater 35c which is disposed above the liquid level H of the liquid ozone stored in the vaporizer 35 and applies heat to the liquid ozone; and a liquid level control section 43 and valves V3, V33 which regulate the height of the liquid level H of the liquid ozone in the vaporizer 35 based on demand of ozone gas from a dissolution section 50.