PURPOSE: To improve heat insulation and temperature recovering speed at the opening of a film forming reaction furnace by constituting a part, which is near either the furnace opening of an external tube or an inner tube which constitute a quartz reaction tube into which a subject to be surface treated is placed, of opaque quartz.

CONSTITUTION: At least a part P tube which includes a flange 24 near the furnace opening 50 of a reaction furnace is constituted of opaque quartz and other parts are constituted of transparent quartz. The tube and other parts are welded so as to be integrated. A cylindrical heat insulating tube 28 constituted of opaque quartz between an external tube 21 and an internal tube 25 is arranged. Thus, the temperature at the furnace opening 50 is limited to be reduced to 730°C after opening a capping flange 40 after film formation, taking out semiconductor wafers and arranging semiconductor wafers of the subsequent batch inside. Therefore, a time required for returning the temperature near the furnace opening 50 to a prescribed temperature, which is approximately 750°C, is shortened.