To prevent a reducing fine powder from adhering to a connecting pipe between a secondary cyclone and a pneumatic feeder by a method wherein a cooling means is arranged at the wall of a reducing particle accumulating section placed at a connecting section between a down-pipe of the secondary cyclone and the pneumatic feeder.

A down-pipe 11b of a secondary cyclone is connected to a down-pipe of a primary cyclone through an accumulating region 12 and a feeding conduit 13, the accumulating region 12 is provided with a fluidizing plate 14, carrier gas is forcedly fed from a lower part of it to cause some particles to be fluidized. Then, a cooling means such as a water-cooled Jacket 15 or the like is arranged in the particle accumulating region 12 at a connecting section between the down-pipe 11b of the secondary cyclone and the pneumatic feeder. In this case, this is made such that there is provided a structure having some thermal insulating materials coated at the water-cooled pipe of the water- cooled jacket 15 or there is provided an air-cooled pipe in which a temperature of the wall is reduced to about 700°C or less, for example, thereby the reducing fine powder is prevented from being adhered to the wall.