JP2937431B

PURPOSE:To accurately discriminate a boundary surface by respectively counting the number of ion exchange resins within a predetermined region in a horizontal direction at many positions in a vertical direction from imaging data and setting a place where large displacement is generated in the count number of resins as a boundary surface. CONSTITUTION:When the boundary surface between the action exchange resin and anion exchange resin settled in an ion exchange resin tower 10 by backwashing separation treatment is detected, the ion exchange resins in the ion exchange tower 10 are imaged by an imaging means 22. The number of the ion exchange resins within a predetermined region in a horizontal direction are respectively counted with respect to a large number of positions in a vertical direction. A place where large displacement is generated in the count number of the resin is discriminated as the boundary surface. As a result, even when the change of reflectivity due to the contamination of the ion exchange resin is generated, no detection error is generated and the boundary surface of the separated ion exchange resin can be accurately discriminated.