PURPOSE: To allow combustion of solid particulate fuel with high efficiency for an extended period by providing an immobile lattice whose main body is a perforated plate which receives the solid particulate fuel and a mobile member for moving a used solid particulate fuel.

CONSTITUTION: A solid particulate fuel 64 comes in a combustion chamber 62 through an opening 98, and then falls on a lattice 112. A rotative arm 70 positioned in a horizontal plane just above the lattice 112 can be rotated in any direction, right or left. The arm 70 so moves as to sweep the upper surface of the lattice 112 to guide a used solid particulate fuel (ash, clinker) into an opening 104 provided on the outer peripheral surface of the lattice 112. The used fuel is pushed out of the opening 104, and falls in a collection tray provided by a combustion pot 54. Thus, accumulation of a lot of used fuel on the lattice 112 is prevented. The arm 70 passes in a burning solid particulate fuel, so that generation of clinker which occurs when impurities are contained in the fuel to raise frame temperature or lower melting-point of the fuel and vitrifiability of the fuel is suppressed.