Abstract: A rapid cooling apparatus passing hot exhaust gas in a short time along a flow path formed in a cooling setting with piled up arrangement and having a reduced cross-sectional area of the flow path to reduce the volume thereof so as to cool rapidly to a temperature below a dioxin synthesizing temperature so that dioxins are prevented from generating, characterized in that multistage tube bodies for heat exchange to pass coolant therethrough are arranged in a rapid cooling cylindrical body for passing hot gas such as exhaust gas from an inlet opening to an outlet opening, and the cross-sectional area of the rapid cooling cylindrical body is being reduced gradually in a passing direction of the hot gas.