PURPOSE: To make it possible to take out high temperature combustion exhaust gas containing no solid ember or ash and capable of being used for drying grains or the like, by burning continuously granular material such as husks or the like as well as centrifuging automatically the embers and ash in a combustion chamber.

CONSTITUTION: A suitable amount of granular material such as chaff or the like is introduced into a combustion passage 14 in an air-permeable furnace body 10 and is fired, in the initial stage of the combustion, the primary air blown from a blowing apparatus 19 is fed by a change-over valve 17 into the combustion passage 14 to burn the granular material therein to the red state, the surplus air is led into an unburned gas combustion cylinder 13 where the unburned gas is burned, and when the upper part of the granular material in the red state filled in the combustion passage 14 has been fluidized like an avalanche toward a surrounding air- permeable wall 7, the change-over valve 17 is operated to open a swirl air chamber 5 so that the secondary air is jetted through a number of openings in the air-permeable wall 7 in the circumferential direction about the axis of the combustion chamber 2 to burn the particle material further as well as to centrifuge the embers and ash.