Abstract: The present invention relates to an apparatus for filtering a liquid through a movable filter bed consisting of granular material, with continuous scavenging of the bed material and having the characterizing functions as follows:the filtering takes place in that liquid from a central inlet passes outward and upward through the filter bed.the filter bed in operation moves continuously downward, and the bed material is renewed continuously by supply to the upper portion (A) of the filter.the separation of impurities in the liquid takes place substantially in the central portion (C) of the filter and to a small extent in the portions located closest to the outlet.the washing of polluted bed material takes place in several steps, the first one thereof by fluidization of the material in the lowermost portion (D) of the filter, and the last one with liquid and air in the upper portion (A) of the filter.