Abstract: A film deposition system which a cycle of alternately supplying a first reactive gas and a second reactive gas and exhausting them is repeated twice or more in a vacuum vessel to cause reaction between the two gases, thereby depositing thin films on substrate surfaces, the film deposition system includes: a plurality of lower members having substrate-placing areas on which substrates will be placed; a plurality of upper members so placed that they face the lower members to form processing spaces together with the substrate-placing areas; a first reactive gas supply unit and a second reactive gas supply unit for supplying a first reactive gas and a second reactive gas, respectively, to the processing spaces; a purge gas supply unit for supplying a purge gas in the period between a first reactive gas supply period and a second reactive gas supply period; exhaust openings, situated along circumferences of the processing spaces, for communicating the inside of the processing spaces with the atmosphere in the vacu