PURPOSE: To facilitate the regeneration of a filter and to improve treatment efficiency by discharging fluid after precipitation of solid in the lower part of a solid separation cylinder and discharging the treated fluid passed through a filter in an upper filtration cylinder from a discharge pipe.

CONSTITUTION: A fluid including city water is supplied from a supply pipe 6 to a solid separation cylinder 2 along the tangential line. Solid is precipitated by centrifuging, and the precipitate is prevented from dispersion by buffleplates 7. Treated water after separation of solid is contacted with a filter 3 in an upper filtration cylinder 1 and filtered by passing through filter aid 12 which makes up the filter 3, the space between stacked disks 11, and holes 10a of a horizontal pipe 10 to be discharged from a discharge pipe 4. The treated water, which has not passed through the filter 3, is returned from a return pipe 5 to the solid separation cylinder 2 to be treated again. The filter 3 is regenerated by the back flow of compressed air or pressure water from the discharge pipe 4.