Abstract: An apparatus for filtering raw water comprising a drum composed of disc-shaped end plates, horizontal member or members extended between the peripheries of the end plates, and a water-permeable filter cloth with a long pile stretched round the member or members to form a drum-shaped filter body. A rotating shaft supports the drum and the drum is submerged in a raw water conduit. A discharge pipe communicates with the inside of the drum. A hopper is located immediately below the filter body in the conduit and carries a pair of rolls on its upper edges for contact with the filter body. A drain pipe is connected to the hopper. The arrangement permits efficient removal of minute floating and drifting matter, such as plankton, from raw water, making possible a high rate of filtration with a very small space requirement.