To provide a fire furnace which incinerates garbage without special working and selecting of the garbage nor with addition of auxiliary fuels.

In a fluidized layer type garbage incineration/melting furnace 1 which heats and burns a fuel by heat medium particles using a solid matter or a slurry as fuel, air is supplied from a supply pipe 22 at a speed lower than the minimum fluidization rate of the heating medium at least at a part of the fluidized layer of the fire furnace 1 and at least during one period of the operation of the fire furnace to be burned while at least a part of the fuel is kept collected and the temperature of combustion is set at a melting temperature of ash or above to melt. Melt solidified matter of the ash is withdrawn to be crushed by a crusher 18 and the fluidized layer type garbage incineration/ melting furnace 1, is filled with the particles adjusted by a strainer 19 as part of the heat medium particles.