A water-treating ceramic filter unit comprising a filter having pluralities of flow paths partitioned by porous ceramic cell walls and plugs alternately sealing the one-side or other-side ends of the flow paths; a housing containing the filter such that water to be treated is supplied from one end of the filter, and that the treated water is discharged from the other end of the filter; and seal members disposed on the outer edge portions of both end surfaces of the filter for longitudinally sandwiching and fixing the filter to the housing; the maximum of a gap between a side surface of the filter and the housing being equal to or less than the equivalent diameter of the flow paths.