PURPOSE: To reduce the fouling of a member, and to prevent the decrease in cleanliness due to the rescattering of deposited dust even under high-humidity circumstances by using the member having a resistance to the flow of air and provided with a light transmitting and antistatic membrane.

CONSTITUTION: A member 8 having a resistance to the flow of air is constituted by providing many through-holes 12 to a light transmitting dielectric plate material 11, and covering both sides of said plate material 11 facing the windway and the inner surface of the through-holes 12 with an antistatic membrane 13 consisting of a light transmitting and dielectric composition. The polluted air, after passing through a prefilter 6 wherein coarse dust is removed, is introduced into an HEPA filter 5 through a fan 4, and the purified air is obtained. Then said air passes through the space provided with illuminating lights 7, and reaches said member 8. Then the air is blown out into woring space 2 with a uniform distribution of wind velocities as shown by the arrow (a) due to the rectifying effect of said member. Since said member 8 has light transmissivity, the irradiation of the light of the illuminating lights 7 into the working space is not prevented.