An apparatus for filtering liquids, such as fibre pulp suspensions, includes annular hollow filter discs each of which has two annular liquid pervious, opposed walls covered with filter material, spray nozzle means for cleaning the filter material, and means providing relative movement between the filter material and spray nozzle means. The annular opposed walls of each filter disc are only attached to each other at their radially outer ends, whereas they are spaced from each other at their radially inner ends, such that an annular opening is defined between the interior of the filter disc and a filtrate chamber extending centrally through the filter discs. The spray nozzle means extends from the filtrate chamber through the annular opening into each filter disc. As a result, an extremely pure fine fraction can be produced, clogging of the filtering material is efficiently counteracted, and the operative part of the filter material can be increased.