To improve filtration performance and reliability by making it bearable largely by a pressure difference between the inside and outside of a filtration separation membrane cartridge and increasing deformation resistant force opposing the hydraulic pressure of a raw liquid acting on a filtration separation membrane simple substance and a chemical liquid during backward washing with regard to the filtration separation membrane cartridge, a filtration separation membrane unit, and a filtration device.

In the filtration separation membrane cartridge K1, two corrugated plate-like FRP (fibrous glass reinforced plastic) separation membrane simple substances 1 and 2 which are arranged oppositely at a prescribed distance (G0), a watertight material comprising an adhesive 15 for holding the watertightness of the peripheral parts F1b and F1c of the four sides of the separation membrane simple substances 1 and 2 and each watertight auxiliary cover 16 or 17, and a water discharge pipe 12 for making permeation-treated water Wf flow between a permeation water passage 13 between the filtration separation membrane simple substances 1 and 2 and the outside are provided, and activated sludge water Ws containing impurities is made to permeate through the separation membrane simple substances 1 and 2 to extract the permeation-treated water Wf. The separation membrane simple substances 1 and 2 are composed of a corrugated plate in which the cross section perpendicular to the flow direction of an ascending activated sludge water flow Ws1 is corrugated in the arrangement condition of the cartridge K1.