PURPOSE: To improve the durability and reliability of a stoker by a method wherein solid fuel is fed onto the upper layer of heat insulating material after the heat insulating material has been fed onto the stoker.

CONSTITUTION: Spherical heat insulating materials 6 are introduced from a conveyor 5 onto a stoker so as to form a heat insulating layer, and onto which solid fuel is spread with a spreader unit 2. The heat insulating materials fallen through the stoker 4 roll on an ash separating plate 8 so as to return to the conveyor 5. Because the solid fuel burns on the heat insulating layer, the solid fuel does not touch the stoker 4, preventing the stoker from being cracked due to high temperature corrosion and thermal fatigue and improving the durability of the stoker.