To increase a combustion efficiency by a method wherein an air pipe is provided at the lower part of side surface of an incinerator body in the direction of up-and-down to supply air forcibly while natural air supply is effected simultaneously to increase the amount of naturally supplied air by a vacuum generated by the forced air supply.

Forced air supply is effected by providing an air pipe at the lower part of side surface of an incinerator body in the direction of up-and-down while a space is formed between the lower part of the incinerator body and the surface of installation of the same and a natural air supplying air pipe 13 is provided so as to be neighbored to the air pipe for forced air supply to effect natural air supply and forced air supply simultaneously. A furnace body cooling jacket 6 is provided around the outer peripheral part of the incinerator body, a chimney cooling jacket 7 is arranged around the outer periphery of a chimney and an underground tank 8 is buried below the incinerator while respective tanks are communicated through pipes to conduct the overflowing water of the chimney cooling jacket into the furnace body cooling jacket and conduct the overflowing water of the furnace body cooling jacket into the underground tank. In this case, a water supplying pipe 19 is provided with an automatic opening and closing valve 33.