PURPOSE: To reduce the cost of a facility by partitioning an upper space where a self-propelled bogie is run and a lower space where a driven bogie mounted with a conveyed object is run with a bulkhead, and feeding air from the upper space to the lower space through communicating sections provided on the bulkhead.

CONSTITUTION: Connecting bars 33 are penetrated through a bulkhead 9 partitioning an upper space and a lower space, the sealed state is maintained by lip packings 16a and 16b, a suction blower (not shown in the figure) is operated to keep a conveying path 3 at the negative pressure state, thus an air stream is formed from a suction port 12 to an exhaust main pipe 14 through the upper space, slits 10, the lower space, and an exhaust branch pipe 13. Clean air invariably flows into the upper space from the outside, and no air flows back from the lower space. Even if a sample in a container P located in the lower space is a weak acid material, its adverse effect is not inflicted on the upper space. Countermeasures such as corrosion-resistant processing may be applied only to the lower space with a simple structure.