To reduce the leakage of an exhaust piping in an oxidating/diffusing apparatus.

The oxidating/diffusing apparatus discharges a processed exhaust gas from a reaction tube 16 via an exhaust piping 32. A refrigerator 40 for cooling the exhaust gas flowing in the exhaust piping 32 is disposed on the way of the piping 32. An exhaust piping 33 at the upstream of the piping 32 is made of an anticorrosive and heat-resistive material such as quartz, including the refrigerator 40. An exhaust piping 34 at the downstream of the refrigerator 40 is made of a hard resin such polyvinyl chloride having no heat resistance but a corrosion resistance and a low gas permeability.