PURPOSE: To perform a complete combustion of ignited material, make discharged combustion gas clean and concurrently shorten a time required for the combustion.

CONSTITUTION: A lower stage mounting table 3 having through-pass holes 3a is installed within a main body 1 of an incinerator having its upper surface closed. A primary combustion chamber 4 and a secondary combustion chamber 5 positioned below the primary combustion chamber are defined and formed within the main body 1 of the incinerator. A feeding cylinder 17 is fixed to a discharging port 16 arranged in correspondence with the secondary combustion chamber 5. An inner part of the feeding cylinder 17 is applied as a third combustion chamber 18 communicated with the secondary combustion chamber 5. Each of combustion chambers 4, 5 and 18 is provided with air nozzles 9, 10 and 19 for supplying air to the chambers. A discharging tower 31 is vertically arranged to be adjacent to the main body 1 of the incinerator. A duct 32 for use in feeding combustion gas with the third combustion chamber 18 to the discharging tower 31 is arranged between the main body 1 of the incinerator and the discharging tower 31. A heat exchanger 33 is installed within the duct 32. When the ignited material on a mounting table 31 is to be ignited, combustion gas generated passes through the primary combustion chamber 4, the secondary combustion chamber 5, the third combustion chamber 18, the duct 32 and the discharging tower 31 and then the gas is discharged out of the incinerator.