liquid enters the filter from the inlet and flows inward from the outer surface of the filter element. The lower end of the filter element (wedge wire screen) is connected to the outlet, and the liquid flows out from the outlet. When a certain amount of impurities are intercepted on the surface of the filter element(wedge wire screen), the cleaning procedure is started at a fixed time or according to the set pressure difference. The reduction motor drives the scraper blade obliquely attached to the outer surface of the filter element to rotate and scrape off the impurities on the outer surface of the filter element (wedge wire screen) . The impurities leave the surface of the filter element (wedge wire screen) along the scraper and fall into the bottom of the filter with the descending liquid. The rotating sweeping plate sweeps the heavy impurities at the bottom into the sewage collecting chamber. The impurities accumulate in the sewage collecting chamber and the bottom of the filter. The drain valve opens automatically at a fixed time to discharge the liquid containing high-concentration impurities from the drain port. If necessary, the discharged residual liquid can be recovered.