Abstract: The present invention provides a hollow-fiber filter module comprising a straight tube, a bundle of hollow fibers having at least a part thereof disposed within the straight tube, a fastening member for bundling and fixing the open ends of the hollow fibers, and at least a branch tube having an end protruding to the outside of the straight tube, that surface of the fastening member which includes the open ends of the hollow fibers being attached to the branch tube in a fluid-tight manner, as well as a filtration method in which a plurality of such hollow-fiber filter modules are connected in series to form a filter module assembly and a fluid to be treated is filtered by utilizing one end of the connected straight tubes of the assembly as an inlet for the fluid to be treated, the other end thereof as an outlet for the fluid to be treated, and the branch tube of each module as an outlet for the filtered fluid.

Abstract: The ornamental design for a filter, as shown and described.