A processing chamber having a heating device for heating the interior thereof to a required temperature, and a holding device with at least three separate holding elements is disclosed. A processing gas feed port and processing gas passages are provided in a cap which is connected to a processing chamber and closes an opening in the upper surface of the processing chamber, and the processing gas feed port and the processing gas passages are connected by a connection pipe. The processing chamber is connected to processing gas sources and has processing gas introduction passages formed in a side wall thereof and communicated with the processing gas passages. Seal members are provided around open ends of either of the processing gas passages or the processing gas introduction passages in the surfaces of the processing chamber and the cap opposed to each other. Thus generation of particles can be precluded in the processing gas feed unit, and smooth supply of processing gases, improved yields and throughputs, and easy maintenance operation can be attained.