A dielectric 13 is provided on each of opposing surfaces of a pair of electrodes 14. Discharge gaps 20 communicating with a raw material gas supply path and an ozone gas removal path are formed between the pair of dielectrics 13. A functional film 17 is formed on each of the pair of dielectrics 13 so as to face the discharge gaps 20. The functional film 17 contains a first metal oxide of one or more metals selected from a group consisting of niobium, tantalum, molybdenum, and chromium, and a second metal oxide of one or more metals selected from a group consisting of titanium, tungsten, zinc, and iron.