The invention relates to a filtering apparatus including, inside a filtering tower (1), a filtering section (r), a liquid collecting section (7) and a liquid feeding section (e). The liquid feeding section (e) includes a diffuser (A) attached to an upwardly oriented orifice (5a) formed at a leading end of a liquid feeding pipe (5). The object is to provide an apparatus which allows use of the existing filtering tower without its enlargement and which allows uniform falling of the filtering liquid over the substantially entire top surface of the filter medium layer, thus making it readily possible to maintain the flatness of the top surface of the filter medium layer even when light-weight medium is employed, thereby to allow the filter medium layer as well as the entire filtering apparatus to achieve their desired filtering performance. The diffuser (A) includes a damping portion (k) for damping the momentum of the liquid discharged from the orifice (5a), a first discharging portion (8) for upwardly discharging the liquid damped by the damping portion (k), a second discharging portion (9) for laterally discharging the liquid damped by the damping portion (k), and a third discharging portion (10) for downwardly discharging the liquid damped by the damping portion (k), said first, second and third discharging portions being stacked one on another from the top to the bottom in the mentioned order.