Abstract: The present invention discloses a CVD apparatus which, together with being able to efficiently perform purging treatment after maintenance, uses for the purge gas a mixed gas of a gas having high thermal conductivity and an inert gas during heated flow purging treatment after maintenance to perform startup of the CVD apparatus while reducing the amount of time required for purging treatment. Purging treatment before semiconductor film formation is performed by repeating the pumping of a vacuum and the introduction of inert gas a plurality of times.