The invention relates to a stepped filtration device (1) for mechanically separating solids from liquids flowing through channels, gutters or pipes. The inventive device has numerous step bars (7') connected in a fixed grid (7) and numerous step bars (6') connected in a mobile grid (6). The grids (6, 7) are positioned inside the stream of liquid, and are inclined in the direction of flow, starting from a level below the surface. The step bars (6', 7') form a stepped arrangement in the direction facing the incoming flow. The mobile grid (6) can be activated by a drive device (8) on a track which, starting from a zero-position identical to that of the fixed grid (7) in a vertical and horizontal direction, permits a stroke movement upwards over the steps of the step bars connected in the fixed grid (7) and towards the direction facing the incoming flow, at least as far as a position identical to that of the next highest step bar of the fixed grid (7) in a vertical and horizontal direction, and which then guides the step bars (6') of the mobile grid back (6) into the zero-position below the fixed grid (7). The fixed grid (7) is surrounded at least at the sides by frame parts (3, 4). The invention is characterized in that all of the drive elements (11, 12, 19, 13) of the mobile grid (6) are located essentially in the common level formed by the fixed grid (7) and the mobile grid (6) in the zero-position.