PURPOSE: To reduce the operating quantity of a blower by connecting dust throw-in equipment of each region to a dust-air separater of a collecting center through a dust conveying pipe and providing a temporary dust storing tank, a vacuum holding portion, and a dust compressor under the dust-air separator in order.

CONSTITUTION: Dust which is thrown in each region, together with air is introduced into a dust-air separator 5 through a dust conveying pipe 4 to separate dust from the air. The separated dust is stored in a temporary storage tank 15. At this time, a dust compressor 6 is separated form the temporary storage tank 15 and dust-air separator 5 by a vacuum holding portion 16. A container 7 is connected to the compressor 6 and, when the temporary storing quantity reaches a defined quantity operating a level gauge 18, the gate 20 and damper 23 of the vacuum holding portion 16 are opened to introduce dust into the compressor 6. Then, the compressor 6 compressingly houses the dust into the container 7. Thereby, the power of a blower can be reduced.