To prevent foreign matter such as paper powder from getting mixed into the content by removing the same even if the foreign matter remains in the body of a fiber drum.

After the body 2 of the fiber drum 1 is fed to a hot air supply position through a feeder 12, hot air is supplied into the body 2 of the fiber drum 1 from a hot air device 13 to kill a Psocoptera or the like penetrating into the body 2. Subsequently, the body 2 of the fiber drum 1 is fed to a dust collection position through the feeder 12 to evacuate the body 2 of the fiber drum 1 by a dust collector 14 to suck and remove the deathwatch or the paper powder. After cleaning, the body 2 of the fiber drum 1 is fed out through the feeder 12.