A lower part 14L of a band way 14, which is incorporated in an arch unit 12, is separated from the other parts of the band way 14. A drive means (air cylinder) 35 supports the lower part 14L, allowing the same to move between a substantially horizontal initial position and an inclined position. A band 13 is released from the band way 14 when a packing operation starts. Thereafter, the lower part 14L is moved from the initial position to the inclined position and compressed air is applied to the guide surface 14a of the lower part 14L, thereby removing foreign matter from the band way 14. This sequence of removing foreign matter is performed in, for example, each cycle of packing operation.