At the halfway of the particle extracting pipe 26, a gas affluent pipe 27 is connected therewith.In an apparatus of such a structure, silicon granules (diameter: 0.015.about.0.30 cm) prepared by the silane process are passed into the heating container 21 through the particle inlet pipe 24 and an inert gas such as argon gas is introduced intothe heating container 21 through the gas inlet pipe 27, w