PURPOSE: To provide a filter unit prevented from the reduction of a filtering area generated from the mutual interval nonuniformity or strain of laminated filter segments caused by the assembling inferiority of the filter unit or the swelling of a filter material by interposing grommet supports between the filter segments, hardly damaged by the back pressure caused by backwashing and effectively usable from the beginning of filtering operation to the final stage thereof.

CONSTITUTION: A filter unit 1 is constituted by laminating filter segments 2 wherein the outer peripheral edge overlapped parts of filter sheets 8 opposed each other through support screens 7 forming filtrate passages and having liquid passing ports at the central parts thereof are sealed by thermoplastic resin seal rings 3 so that the liquid passing ports are allowed to communicate each other through center rings 5. Grommet like supports 4 having height exceeding the top surfaces of the sheets 8 at the parts holding the surfaces of the sheets 8 under pressure at the predetermined angle interval between the seal rings 3 and center rings 5 of the segments 2 are provided in a liquidtight manner.