To remove foreign matters mixed with flowing cereal grain, flour or fruits by capturing with an apparatus of the outside of a flowing path.

Five cylindrical magnets 22 are housed in a row with spacers 23, ... disposed between six housing cylinders 6, ... mounted on the outside of an isolation cylinder P. The magnets 22 are arranged in such a manner that each of N poles is faced and approached to each of other N poles or each of S poles is faced and approached to each of other S poles. Therefore, the magnetic force of the magnet 22 does not absorbed in the other magnet 22 to effectively transmit the magnetic force of the magnets 22 through the isolation cylinder P into the flowing cereal grain or fruits, so that the foreign matters in the cereal grain or the fruits are surely removed and the removed foreign matters are surely sucked and absorbed on the surface of the isolation cylinder P.