PURPOSE: To improve the combustion efficiency and to completely burn a liquefied fuel by introducing air into a tubular fire grate from the flue side, and ejecting heated air at a predetermined angle through nozzle arranged to the direction of a furnace-cylinder side.

CONSTITUTION: Air introduced into a fire grate 15 in the direction shown by arrow 18 obtains combustion heat and is ejected through nozzles. Air in an upper nozzle 16 raises the combustion efficiency of a fuel 12. Further, a combustion gas is blown into the furnace cylinder and the back flow of the combustion gas is prevented to improve the stack effect. Ejected air from a nozzle 17 promotes the combustion of charcoal which has dropped in the form of charcoal fire, and further blows ashes generated into an ash collector 19. Flame of firewood does not rise upward but is flowed laterally so as to successively burn the entire firewood from the downward. A liquefied resin system fuel 21 which has flowed down is gasified in an ash reservoir 8 via high-temperature air, and completely burned.