Abstract: To prevent contamination of a substrate by natural oxide film etc in the inside-apparatus transfer period, a CVD apparatus is provided with a wafer deposition part 10 and a wafer transfer part 30. Wafer transfer part 30 includes cassette mounting bases 31(1), 31(2), 31(3), 31(4), wafer transfer chamber 32, cover opening/closing mechanisms 33(1), 33(2), 33(3), and 33(4) and a wafer transfer robot 34. Transferring of a wafer 51 between cassette 52 mounted on cassette mounting bases 31(1), 31(2), 31(3), 31(4) and water deposition part 10 is performed through a sealed space provided by wafer transfer chamber 32. This sealed space is cleansed by inert gas by means of a vacuum evacuation line 35, inert gas supply line 36, oxygen concentration detector 37 and control part 38.