To provide a coal burning boiler which generates a combustible gas from an organic waste such as plastic, and uses the generated combustible gas as a fuel for the coal burning boiler, and also to provided an organic waste gasification furnace and a coal ash treating plant for fusion-treating coal ash generated from a combustion part of the coal burning boiler and from an economizer thereof by the gasification furnace for forming gasification.

There are provided the coal burning boiler, organic waste gasification furnace and coal ash treating plant. The coal ash generated in the coal burning boiler is supplied to a fusion area inside the gasification furnace, in the gasification furnace for fusion-treating the organic waste such as plastic, so as to treat continuously the coal ash with high efficiency. The combustible gas rich in carbon monoxide and hydrogen generated in the gasification furnace is supplied into the coal burning boiler at the same time and burned mixedly as fuel to use effectively the gas generated in the gasification furnace.