PURPOSE: To improve combustion characteristic and to maintain stable combustion condition in the dust incinerator in which combustion air is fed from the downward of a fire grid by increasing or decreasing all or a part of the combustion air intermittently.

CONSTITUTION: The dust incinerator burns dust thrown into a hopper 2 while moving and drying the same on drying fire grids 3 and 4 and a combustion fire grid 5 in this order. In this instance, the air for drying and burning the dust is fed by a fan 7 below the fire grids 3 to 5 through an air prewarmer 8. In the incinerator of the above construction, a function generator 11 is connected to a drive means of a damper DT which controls the total amount of the combustion air. The function generator 11 generates intermittent signals which drive the drive means intermittently. By this, the total amount of the combustion air can be increased and decreased intermittently, thereby improving the combustion characteristic and maintaining the stable combustion condition.