To solve the problem in a secondary combustion air introduction method intended for perfect combustion in a secondary combustion chamber to reduce the environmental load of exhaust gas in a waste incinerator that a structure for mixing exhaust gas after primary combustion with air is complicated, and the perfect combustion cannot be ensured.

In this air introduction method, an ascending kiln-like introduction pipe is adapted to efficiently introduce primary combustion exhaust gas to a reheating position within a secondary combustion chamber, and as an exhaust smoke funnel part, a double structure smoke funnel is adapted to take secondary combustion air and tertiary combustion air.