PURPOSE: To prevent fires from breaking out in a treating device for wastes unsuitable to be burned which contain waste plastics or the like, by a method wherein when the temperature of a circulating line for a heating gas exceeds a preset temperature, a sprinkling valve is opened to sprinkle water to the interior of a rotary cylindrical body and a lightweight waste accumulating site.

CONSTITUTION: The heating gas discharged from a heating gas generating furnace 8 is introduced into the interior of the rotary cylindrical body 5 through an introducing hole 9, whereby it is brought into contact with solid city wastes containing synthetic high molecular materials, and is taken out into the circulating line 10 through a fixed cylindrical body 1. When the lightweight waste is ignited and an abnormal temperature rise is detected by a thermometer 14 provided in the line 10, the sprinkling valve 15 is opened to eject water through sprinkling nozzles 13.