An incubator includes filters in supply passages for supplying an environment-adjusting-medium. Divergent passages are connected to portions of the supply passages upstream from the filters. The divergent passages converge to a single supply/exhaust passage, which is provided with a pump. By driving the pump in a forward or reverse direction, decontamination gas is pumped from a culture space and discharged outside, and open air is introduced into the culture space. After sucking the contamination gas to adsorb it on the filter, open air is introduced so that the contamination gas is discharged into the culture space 6.
