PURPOSE: To provide an energy saving by a method wherein a purifying means is arranged at a ceiling surface of an upper part of a target region having a high degree of cleanliness and a surrounding region of the purifying means is provided with a surrounding area blowing port of which flow passage is metered so as to form an air flow layer having a higher sir speed than an air flow speed in the region of high degree of cleanliness.

CONSTITUTION: Within a target region of a high degree of cleanliness, a part of air within a space 3 of a ceiling part is blown by an air blower 11 to a filter 10 and a surrounding region blowing port 13. Air flow passed through the filter 10 flows down in the target region of high degree of cleanliness at an air speed V1. Concurrently, and air speed V2 in air flow layer blown from the surrounding region blowing port 13 around the filter 10 flows down at a faster air speed than the air speed V1 of the air flow in the region of high degree of cleanliness, resulting in forming an air curtain between it and an area out of target region of a high degree of cleanliness within a clean room. Dust are merged into the air flow in the surrounding region so as to prevent the region of a high degree of cleanliness from being influenced by the dust. The air flow flowed down the region of a high degree of cleanli ness enter from a floor 5 having some holes into an under-floor space 6, enter from a duct 8 into the ceiling space 3 and then circulates. Accordingly, an air flow control device may easily be adapted for a modification in layout of a manufacturing device and it is not neces sary to increase a degree of cleanliness within an entire room, so that it is possible to provide an energy saving.