To provide a dust removing device of hydraulic power system with a simple power transmission mechanism.

A screen 2 is installed paralleled to an intercepting pipe on a weir arranged between the intercepting pipe in which rainwater and sewage from a joining type sewerage flow and a discharging pipe which joins revers. On the intercepting pipe side of the screen 2, a scraping device 3 with a driving body which actuates garbage scraping rake 12 vertically along the screen 2 is installed. On the intercepting pipe, a waterwheel 4 with a rotary shaft perpendicular to the flow of the intercepting pipe is installed. The waterwheel 4 and the driving body of the scraping device 3 are coupled by a flexible shaft 6. The waterwheel 4 is in a changeable height using moving parts 32, and when the water level of the sewage is low, it is positioned in the height avoiding flood. Therefore, the water wheel 4 turns only when the water level inside the pipe is heightened by heavy rains or so, transmitting the power to the driving body through the flexible shaft 6, giving the scraping device 3 satisfactory drive.