To solve a problem wherein an incomplete combustion tendency exists in a conventional simple incinerator, because a function for a gasification process for taking out combustion gas from an organic substance is not provided in the conventional simple incinerator.

This incinerator provided with a B combustion chamber is used in an upper portion of an A combustion chamber. The first combustion process for burning the combustion gas together with introduced outside gas in the A combustion chamber and the second combustion process for burning again the residual combustion gas in the B combustion chamber held at 800°C or more of high temperature provided with an auxiliary combustion means are executed respectively in an after process of the gasification process for taking out the combustion gas from the organic substance.