[en] Filters after collecting particulate radioactive materials are discharged passing through a path and contained in a bag mounted to a discharge opening of the path. The inside of the bag for containing the filters is evacuated after sealing the path by a partition valve. Then, it is sealed in the vicinity of the mounting portion by a sealing means. Accordingly, the filters after collection can be recovered in a state sealed in the bag without contaminating surrounding air, to ensure environmental cleanness. Further, since the volume of the bag for containing the filters is reduced by compression, transportation, subsequent measurement for the mass of radioactive materials and processing of wastes are facilitated. In particular, if a thermoplastic film is used for the sealing bag, it is melted under heating and sealed by a heat melting type sealing means, thereby enabling to facilitate the procedures and reducing the cost. (T.M.)