PURPOSE: To obtain burning method of solid, through which fuel is burnt effectively even if powderly wolid is mingled with it, by pelletizing the unburnt solid contained in an exhaust gas, and burning in a combustion furnace.

CONSTITUTION: Massive solid in a solid fuel is supplied into a combustion furnace 1 through a fuel supply device 2. On the other hand, powderly solid is sent to a pelletizing device 7 through a transportation means 10. The unburnt solid within exhaust gas from the combustion furnace 1 is collected by an unburnt solid collector 4, and sent to the pelletizing device 7 through the transportation means 5. In the pelletizing device 7 the mixture of the solid and the powdery solid are made into a pellet form which is sent to the combustion furnace 1. Thus, even if a large quantity of the powdery solid is contained in the fuel it is used as fuel and its combustion efficiency is improved, too.