To increase the uses of low carbon ash by classifying fly ash in several stages, improving the blaine value of the low carbon ash and improving the removing effect on unburnt carbon.

The particles of the fly ash are made to collide with each other, pulverized and centrifugally classified into high carbon ash and the low carbon ash by centrifugal force. Then, by utilizing the difference of charge polarities of the unburnt particles and completely burnt particles of the high carbon ash frictionally charged at the time of the collision and pulverization of the particles of the fly ash with each other and friction with a pulverizer inner wall, the completely burnt particles and the unburnt particles are separated and drawn and electrostatically classified into low carbon fine powder ash and high carbon fine powder ash.