PURPOSE: To improve carrying efficiency, by arranging two units of upper and lower movers movably forward and backward on rails for carrying carriers, and by arranging the carriers for carrying wafer cassettes, respectively on both the movers.

CONSTITUTION: The whole unit of rails 11 for moving carriers is formed in the shape of a box and divided-inside into two chambers 13, 14 of upper and lower sections with a partition wall 12. A stator 19 composed of a core 19a and a winding 19b is contained in the upper chamber 13, and is set on the upper section of the partition wall 12. A mover 20 having a core 20a and a conductor section 20b is positioned on the upper section of the stator 19, and is set movably forward and backward via wheels 21 on the partition wall 12. A carrier 23 with a wafer cassette 7 mounted on is fitted on the upper section of the mover 20 via an arm 24. The lower chamber 14 and a carrier 29 are also symmetrically composed on the upper and lower sections to form the same composition. Accordingly, with one unit of the rails 11, a plurality of the semiconductor wafer cassettes 7 can be carried at a stroke.