After silicon nitride films have been formed on wafers by a film forming process in a reaction vessel, the reaction vessel is processed by a purging process specified by a purging recipe and compatible with the film forming process to suppress production of gases and particles by removing surface parts of films deposited on the inside surface of the reaction vessel and causative of production of gases and particles.A wafer boat 25 holding a plurality of wafers W is loaded into a reaction vessel 2, and the wafers W are processed by a film forming process specified by a film forming recipe 1 specifying, for example, Si2Cl2 gas and NH3 gas as film forming gases. Subsequently, a purging recipe 1 specifying a purging process compatible to the film forming process is selected automatically, and the reaction vessel 2 is processed by the purging process specified by the purging recipe 1. A purging recipe is selected automatically from a plurality of purging recipes specifying purging processes respectively compatible with film forming processes. Unnecessary extension of purging time is suppressed and the reaction vessel 2 can be processed by an appropriate purging process compatible with the film forming process.