To prevent the local clogging of a filter membrane and to maintain the filterability for a long period by detachably providing a cylindrical structure shorter than a cartridge filter on the pedestal of the cartridge filter with the bottom liquid-tightly fixed in a filter vessel in the downstream hollow part of the filter, passing the liq. passed through a filter membrane between the outer periphery and inner periphery of the plural structures and recovering the liq.

The upstream side of a filter membrane 6 is in contact with a liq. to be filtered, and the liq. passed through the opening 51 for the liq. in an outer peripheral guard 5 is filtered into the downstream side of the membrane 6 from the upstream side and introduced into a space 32 formed by the outer periphery of a cylindrical structure 31 and the inner periphery of a cartridge filter through the liq. collecting opening 52 of a core 7. The filtrate is sent upward in the space 32, passed through the filtrate passages 33 and 34 and recovered through the filtrate opening 12 provided in a pedestal 13. The filtrate introduced into the space 32 is forced up to the height of the passage 33, the liq. positioned at the relatively low part is put under the higher pressure than the liq. positioned at the upper part, and the fluxes of the liq. passing through the membrane 6 are almost equalized regardless of the positional relation. Consequently, the service life of the membrane 6 is prolonged, and the filtration cost is reduced.