Abstract: A clean room suitable for use when ultra high cleanliness of air is to be maintained. The clean room has a ceiling (23), a floor (28), an indoor space (30) between the ceiling and the floor, an air supply means (24) for supplying the air of ultra high cleanliness to the indoor space, and an air exhausting means (40) for exhausting the air supplied to the indoor space. The indoor space is divided into a first region (B) requiring high cleanliness and a second region (A) adjacent to the first region and requiring ultra high cleanliness higher than that of the first region. The air supply means includes an air outlet port (26) arranged in a ceiling of the second region (A) and blowing the air downward, and the air exhausting means includes as first air inlet port (25) arranged in a ceiling of the first region and exhausting the air upward.