PURPOSE: To treat raw water efficiently under high raw water pressure by depositing fine powder on the outside surface of a porous supporting plate formed with many parallel line grooves to make a supporting plate for dynamic membrane and superposing plural sheets of such supporting plates.

CONSTITUTION: Many line grooves 10 are formed on one side of a flat plate of a square shape consisting of porous ceramics or a sintered metallic body in parallel with one side, and fine powder 11 of inorg. materials such as ZrCl4, ThCl4, FeCl3 or org. materials such as fumic acid, polyvinyl pyridine, polyglutamic acid having ≤0.5μ average grain size is deposited on the outside surface of said base plate. Plural sheets of such dynamic membrane supporting plates (a) are superposed in such a way that the grooved sides thereof are positioned upward and the directions of the line grooves of the adjacent supporting plates differ with each other. The laminates are put in a box-shaped pressure vessel and raw water is forced into all the line grooves in one direction. The water permeated through the other line grooves in the different direction is removed from the side surfaces adjacent to said surfaces.