To remove fine, soft and nonsolid floating dirt contained in sewage by a simple physical method.

Fine, soft and nonsolid floating dirt is caught by screens 3 separated and removed by providing a plurality of sheets of screens 3 with fine mesh width for the same flow rate and making the passing area to a plurality of times and gently reducing the velocity passing through the screens. Then, when dirt removing operation is continued for long time, refuse is stuck to the screen parts and passing resistance is gradually increased and a water level is slowly raised. An inflow port is closed by the signal of a high water level detector and a drain outlet 6 is opened to perform drainage. The front and the rear, the upper and lower parts of the screens are cleaned by a high- pressure water spray to remove dirt. After cleaning is finished, the drain outlet is closed an the inflow port is opened to again fill a tank with water and dirt- removing operation by the screens is performed.