A step of constantly supplying first and second carrier gases into a processing container having a substrate therein through first and second carrier gas flow paths, respectively, and supplying a source gas into the processing container through a source gas flow path, a step of purging the source gas by supplying a purge gas into the processing container through a purge gas flow path provided separately from the carrier gas, a step of supplying a reactant gas into the processing container through a reactant gas flow path, and a step of purging the reactant gas by supplying a purge gas into the processing container through the purge gas flow path are performed in a predetermined cycle. An additive gas having a predetermined function is supplied as at least a part of the purge gas in at least one of the purging steps.