Résumé dans la langue de publication, traduction non disponible (Problem) To conduct dust collection in vacuum/reduced pressure refining treatment, using a low cost filter without causing the filter to damage, burn, etc. (Solving Means) Vacuum/reduced pressure refining vessel 1 is connected to dry type dust collector 3 using filter 2 by upstream duct 5, and dry type duct collector 3 is connected to reduced pressure evacuating apparatus 4 by downstream duct 6 and block valve 7 is provided in upstream duct 5. At the start of vacuum/reduced pressure refining treatment, a non-oxidizing gas is injected into the upstream duct upstream of block valve 7 to substantially replace the oxygen in the upstream duct and then hermetically close the upstream duct. After the hermetically closed state has been established in the upstream duct, block valve 7 is opened and dust collector 3 is started to operate. At the end of vacuum/reduced pressure refining treatment, block valve 7 is closed and only the non-oxidizing gas is injected into the upstream duct to return the pressure and then the upstream duct is made open to the atmospheric air, and preferably an open port siding with dust collector 3 is closed in a waiting period from the end of vacuum/reduced pressure refining treatment to the start of next vacuum/reduced pressure refining treatment.