A method of detoxifying an exhaust pipe in a film forming apparatus configured to supply a raw material gas contending a harmful component and a reaction gas capable of generating a harmless reaction product by reaction with the raw material gas into a process chamber to perform a film forming process on a substrate while independently exhausting the raw material gas and the reaction gas from a raw material exhaust pipe and a reaction gas exhaust pipe connected to the process chamber, respectively, is provided. The method includes supplying the reaction gas into the raw material exhaust pipe to detoxify an interior of the raw material exhaust pipe during a predetermined period in which the film forming apparatus is operated and the film forming process is not performed.