To detect even a slight leak of processing soln. by setting a treating tank away from a floor and irradiating the floor with a light beam.

A treating tank 10 is set on a partial foundation 14 through an H bean 16. Accordingly, a space 18 free of pipelines, etc., is secured below a tank 10, a floor 12 under the tank 10 is not covered with pipelines, etc., and the floor can be seen at all times. Further, the floor 12 below the tank 10 is lit up by the light emitted from an illuminator 20 toward the operation side (passage side). Accordingly, when the processing soln. is accidentally leaked out of the tank 10 over the floor 12, the leakage is easily detected from the passage side by the daily inspection.