An ozone generating apparatus produces highly pure ozone gas which can be used in a semiconductor manufacturing process. The ozone generating apparatus comprises a high voltage source, an ozone generating cell which generates ozone gas by supplying a material gas while applying a high voltage from the high voltage source, and a passage for delivering the generated ozone gas from the ozone generating cell to a desired location. The passage comprises a material which has a passivation film formed by a passivation treatment in a dry process. The oxide passivation film comprises chromium oxide film, iron oxide film or a composite film of chromium oxide and iron oxide.