To lower the consumption of materials and the amount of industrial wastes by separating a filter and a core body, making the filter and the core body mutually attachable and detachable, and supporting the filter by supporting the core body uprightly in a base of a filtration case.

A filtration case 21 is installed in a middle of a polishing liquid flow pipe 16. The filtration case 21 is produced by attaching a container-like cover 23 to a base 22 to be connected to the flow pipe 16 in a detachable manner and opening a flow inlet 22a and a flow outlet 22b of a polishing liquid in a center part and an outer circumferential part of the base 22. A cylindrical filter 25 made of a filter material and a core body 28 to be fitted in the axial center part of the filter 25 for reinforcing the inner circumference of the filter 25 are made to be separate bodies mutually attachable and detachable. While being fitted with each other, the filter 25 and the core body 28 are housed in the filtration case 21 and the core body 28 is uprightly supported in the center part of the base 22.