In the present invention, a gas flow rate adjustment apparatus that outputs a raw material gas to an ozone generation apparatus is provided. The gas flow rate adjustment apparatus includes a plurality of flow rate adjustment parts, and outputs a second mixed gas serving as the raw material gas to the ozone generation apparatus. The second mixed gas includes an oxygen gas outputted from a first oxygen flow rate adjustment part and a first mixed gas outputted from a mixed gas flow rate adjustment part. The raw material gas generated by the gas flow rate adjustment apparatus, which includes an oxygen gas and a nitrogen gas, contains the nitrogen gas added to the oxygen gas with the rate of addition being in a range of more than 0 PPM and not more than 100 PPM.