To provide an incinerator wherein an air flow speed entering a furnace from an interstice is increased with simple processing and it is durable to high temperature and has strong spiral flow effect.

The incinerator comprises a furnace body (21), an air box (23), an exhaust tube (24), a number of air fan apparatuses (25), and a number of furnace floors (26). A number of open holes (215) are formed, having a vertical normal line and a proper inclination against a furnace wall surface, and a plug structure (22) is mounted and fixed in the open hole (215), and further an interstice is provided which size is gradually reduced as it goes to its tip end. A spiral protruded edge (222) or a recessed groove is provided on or in an inner peripheral wall of the interstice (221).