To solve such a problem that wastewater mixed with ground refuse or cut refuse generated by machining such as dicing or the like is treated heretofore by two ways of a flocculation and sedimentation method and a combining filtration and centrifugal separation but the reutilization of filtered water can not be performed in the former because chemicals are mixed with filtered water and a system becomes large in the latter, and initial cost and running cost are high.

A second filter membrane 36 becoming a laminated layer containing Si is formed on a first filter membrane 31 comprising a polymer and wastewater containing refuse of Si or glass is filtered by these filters. External force such as air bubbles or the like for preventing clogging is applied to the second filter membrane 36 to keep filtering capacity. Thereafter, the concentration of the wastewater in a raw water tank can be increased.