A device for filtering a processing liquid in a processing tank includes an opening for recovering a surface-layer processing liquid on a work-discharging side of the tank, a separating part for recovering an intermediate-layer processing liquid on a work-receiving side of the tank, a hopper for recovering a bottom-layer processing liquid on a bottom surface on the work-receiving side, a first processing liquid discharge nozzle on a bottom surface of the tank and which is oriented in an opposite direction to a work-conveying direction and toward the bottom surface, second processing liquid discharge nozzles on both side surfaces of the processing tank and which are oriented in an opposite direction to the work-conveying direction and toward a work, cyclone devices which filter the processing liquids recovered by the opening, the separating part, and the hopper, and which individually separate foreign material, a separating tank, and a screw conveyor.