To provide a clean bench according to class IIA, IIB1, IIB2 and IIB3 of JACA standard which is excellent in productivity and suitable for cost reduction.

In a clean bench, an air supply/exhaust unit 21 satisfying JACA standard and a standardized work room unit 1 are provided with a structure jointly connectable by using a connection structure in which a screw or welding is employed. In a connection part 3 of the both units, the space between the air supply/exhaust unit 21 including a work space and the air supply/exhaust unit 21 selectably configured is made negative pressure area to a space around the clean unit 1.