A processing apparatus is provided with a reaction furnace for subjecting semiconductor wafers, which are objects to be processed, to a predetermined processing; a storage rack for storing carriers (wafer cassettes), each containing a predetermined number of semiconductor wafers; and a conveyor for conveying the carriers into and out of the reaction furnace and the storage rack. In this case, a second conveyor mechanism, which comprises the storage portion and at least part of the conveyor, and a third conveyor mechanism are disposed within a sealed chamber in such a manner that they are isolated from the outer atmosphere. An exchange chamber that can be isolated from the outer atmosphere is further provided, for temporarily storing carriers that are to be conveyed into or out of the storage portion, through the sealed chamber via a communicating port. The interiors of the sealed chamber and the exchange chamber are formed so that they can be supplied with nitrogen. This ensures that unprocessed and processed semiconductor wafers can be held in an inert gas environment, so that contamination of the semiconductor wafers by organic substances and heavy metals can be prevented.