Abstract: A filter is spread over each side of the strainer casing rotated by a horizontal driving shaft, and a plurality of radially extending partition plates are provided in the inside peripheral part of said casing, whereby alien matter such as sludge contained in the liquid supplied into said casing is separated by said filters. The alien matter such as sludge remaining in the casing is moved upwardly with rotation of the casing and then dropped gravitationally into a chute-like passage and thereby discharged out of the casing.