To improve combustion efficiency by preventing consolidation caused when drying and burning a substance with high viscosity and a moisture content and spreading it in a rotary kiln.

A spiral steel strip is set higher than heat resistant steel 4 within combustion product input and drying ranges of the rotary kiln. The steel strip is divided into several parts so as to correspond to extension and contraction following a temperature change of a furnace body, and the front and rear steel strips are installed in a lapped state with respect to the rotating direction of the rotary kiln. By this, consolidation is prevented since the inputted substance is spread by the rotation of the steel strip, the mixing of combustion air is promoted, and the combustion efficiency is improved.