PURPOSE: To effect concentration and filtration in the same water tank by preventing blocking of filter cloth due to backwashing and promoting sedimentation of suspension particles by voltage application.

CONSTITUTION: A filter cylinder 2 with one end closed and the other end opened placed in a water tank 1 is covered with a filter cloth 3. A joint pipe 4 installed on the side wall of the water tank 1 is connected with a pressure feed pipe 6 and a discharge pipe 7 through a change over valve 5. The pressure feed pipe 6 is connected to a pressure pump 6a to flow water, etc., back into the filter cylinder 2. An electrode 9 connected to a power source 10 is attached under the filter cylinder 2 so that the cylinder 2 can serve as the electrode when the direct current is applied.