v 7 are closed as shown in fig3 d to cut off the circulating line l 3 from the washing tank 10 to the filtering tank 16 and the circulating line l 4 from the filtering tank 16 to the washing tank 10 in the other hand the switching valves v 8 v 9 in the detergent returning line l 5 are opened as shown in fig3 e in the next when the switching valves v 6 v 7 are closed and the switching valves v 8 v 9 in the contaminated detergent return line l 5 are opened the contaminated detergent is supplied to the contaminated detergent tank 17 through the contaminated detergent return line l 5 in the meantime the switching valves v 1 v 2 is opened and detergent mixed by the detergent and rinse from the detergent tank 11 and the rinse tank 12 is supplied directly to the washing tank and the washing is washed after passing the prescribed time the time between t 1 and t 2 in fig3 a is required time that detergent contamination is changing from the prescribed threshold level to the maximum the switching valves v 6 v 7 are opened and the switching vales v 8 v 9 and v 1 v 2 are closed then the initial condition is set again the contaminated detergent sent to the contaminated detergent tank 17 is forwarded at suitable intervals to the distiller 14 through the contaminated detergent return line l 6 the contaminated detergent is heated and vaporized in the distiller 14 and the vaporized gas of the contaminated detergent is forwarded to the condenser 15 to be condensed and liquefied by chiller water the liquefied detergent is.