A grinding water treating apparatus for separating a processing refuse from grinding water used for processing a periphery of an eyeglass lens, the grinding water being introduced from an eyeglass lens processing apparatus, the grinding water treating apparatus includes: a centrifugal separator that includes a dewatering tank having a bottom surface and a side surface and a drive source for rotating the dewatering tank, and springs out the grinding water to an upper portion of the dewatering tank by rotating the dewatering tank; and a drain pipe that introduces the grinding water from an upper portion of the dewatering tank. The centrifugal separator includes a filter arranged at the upper portion of the dewatering tank and having an opening inserted with the drain pipe for filtering the grinding water separated from the processing refuse by a centrifugal force generated due to rotation of the dewatering tank.