Two load lock chambers having a load lock pedestal are provided adjacent to a vacuum process chamber through a vacuum intermediate chamber. A passage opening is provided between the vacuum process chamber and the vacuum intermediate chamber. Two wafer retaining arms are installed between a platen device in the vacuum process chamber and the vacuum intermediate chamber. The two wafer retaining arms are reciprocatingly movable between the corresponding load lock pedestals and the platen device while passing through the passage opening and crossing with an overpass each other at different levels. By retaining an unprocessed wafer by one of the wafer retaining arms and retaining a processed wafer by the other wafer retaining arm, transfer of the unprocessed wafer from one of the load lock pedestals to the platen device and transfer of the processed wafer from the platen device to the other load lock pedestal are performed simultaneously.