palladium storage tank 32 that stores the hydrochloric acid solution containing the palladium flowing from the dhs impregnated resin column 21 a hydrochloric acid tank 33 for platinum that stores the hydrochloric acid solution of 1 mol l to be flown into the ion exchange resin column 22 for platinum on which the above mentioned platinum has adsorbed a platinum storage tank 34 that stores the hydrochloric acid solution containing the platinum flowing from the ion exchange resin column 22 for platinum a hydrochloric acid tank 35 for rhodium that stores the hydrochloric acid solution of 1 7 mol l to be flown into the ion exchange resin column 23 for rhodium on which the above mentioned rhodium has adsorbed a rhodium storage tank 36 that stores the hydrochloric acid solution containing the rhodium flowing from the ion exchange resin column 23 for rhodium and conduits that supplies liquid between the respective columns and or the respective tanks concerning the flow of the palladium elution step the platinum elution step and the rhodium elution step in the structural system as described above in case where the lapsed time for the steps of s 1 to s 7 reaches a predetermined time in step s 8 as described above in fig1 the hydrochloric acid solution containing the thiourea is caused to flow from the hydrochloric acid tank 31 for palladium into the dhs impregnated resin column 21 s 10 this flowing of the hydrochloric acid solution causes the hydrochloric acid solution containing the palladium and thiourea of 0 01 mol l to be stored in the palladium storage tank 32.