To certainly and efficiently remove a dielectric foreign substance by arranging a minus charged plate above a vibratory conveying path and inclining the top of the minus charged plate to the upstream side of the vibratory conveying path.

Five minus charged plates of polyvinyl chloride 20, 22, 24, 26, and 28 are arranged above the conveying face 14 of a vibratory feeder 12. The oblique angle of the minus charged plates 20, 22, 24, 26, and 28 with the conveying face 14 is set to be 75°, 40°, 45°, 50°, and 55°, respectively, when a material to be treated is a preparation of bromhexine hydrochloride fine particles which is an airway mucus dissolving agent. In addition, the space between each minus charged plate 20, 22, 24, 26, 28 and the conveying face 14 is set to be 9 mm, 9 mm, 6 mm, 4 mm and 3 mm respectively. The minus 3 kv is charged in the minus charged plates 20, 22, 24, 26, 28. Thus it is possible to certainly and efficiently remove a dielectric foreign substance.