PURPOSE: To prevent cloggings of a screen by installing an endless link chain including a dust collecting screen in such a manner that the lower end of said chain is directed to the upstream side of a water channel so as to be inclined to said channel and providing a pipe for discharging air bubbles below the screen.

CONSTITUTION: A dust collecting device 100 is formed, wherein an endless link chain 3 provided with a screen frame 4 is driven through a pair of upper and lower sprocket wheels 1, 2. Next, the device 100 is disposed in a water channel in such a manner that it is inclined to the channel, with its lower end directed to the upstream side and the upper end to the downstream side of the channel. An air pipe 50 is provided along the underside of the frame 4 adjacent thereto and a plurality of air outlet ports are provided on said pipe except for a portion thereof near the surface of the water. The frame 4 is driven obliquely upwardly from the lower end to collect dust and discharge it to a trough 10. When a large amount of dust such as jellyfish has been generated and the entire area of the frame 4 has been covered therewith, air bubbles are delivered from the pipe 50 to separate the attached dust, causing it to float, collecting it by the frame 4. As a result, a water passage is ensured, thereby restraining differences of water levels between the front and rear sides of the device to enable safe operation.