On the front end wall 416, there are provided horizontally-supporting-plate parts 419 and 420 for supporting the casing 413 accurately in a horizontal position when placing the casing 413 on a mounting base 418 (see FIG. 12) in such a manner that the longitudinal side thereof extends vertically (namely, in such a manner as to be in a state in which the inserted semiconductor wafer 412 is supported