PURPOSE: To superpose a covering plate to a bottom plate so as not to move an intermediate layer located in a prescribed position of the bottom plate by moving the covering plate so that one side end of the covering plate is separated from the bottom plate by the action of a guiding member until the side end reaches the prescribed position of the bottom plate.

CONSTITUTION: A pushing member 12 is moved in the direction of a conveyer backet 9 and an inclined mounting lid chip 6 is slided on guide bars 10, 11 in the direction of the conveyer backet 9. When the end part of the mounting lid chip 6 in the side of the backet 9 is separated from the guide bars 10, 11, the end surface of the mounting lid chip 6 in the side of guide bar 11 is slided while being contacted with the inner side of the guide bars 11 and that of the backet 9. Since the inner side of the backet 9 is of the same surface as that of the guide bar 11, the mounting lid chip 6 moves in parallel with the guide bars 10, 11 even after a part of the mounting lid chip 9 has been separated from the guide bar 11. The end part of the mounting lid chip 6 in the side of the guide bar 10 is supported by the base of the guide bar 10 until the mounting lid chip 6 is separated from the guide bar 10.