in size as much as the storage length l 3 a manufacturing or operating cost for the wafer transfer device 10 and the negative pressure wafer transfer chamber 11 and further the whole cvd apparatus can be reduced during the charging operation of the wafers from the temporary storage 25 to the boat 79 by the wafer transfer device 10 the boat loading unloading opening 71 is closed by the shutter 72 therefore the high temperature atmosphere of the process tube 75 is prevented from being flowed into the antechamber 64 accordingly the wafers w which have been already charged or in the process of being charged are not exposed to the high temperature atmosphere so that such adverse effects as natural oxidation of the wafers which can be caused by the exposure to the high temperature ambience can be prevented as shown in fig2 and 3 if the predetermined numbers of wafers w are charged to the boat 79 the boat loading unloading opening 71 is opened by the shutter 72 as shown in fig4 thereafter the boat 79 supported by the sealing cap 88 is raised by the elevating stage 85 of the boat elevator 80 thereby being loaded into the process room 74 of the process tube 75 when the boat 79 reaches its uppermost position the boat loading unloading opening 71 is closed by being sealed by the periphery of the top surface of the sealing cap 88 supporting the boat 79 so that the process room 74 disposed in the process tube 75 becomes in a hermetically closed state since the antechamber 64 is evacuated to be in a vacuum condition and therefore oxygen and moisture are removed therefrom before starting the loading process of the.