To prevent dioxins from being produced in the case of treating contaminants such as soil containing organic volatile materials such as oils, and to efficiently treat the contaminants.

In two heat storage combustion chambers 10a and 10b equipped with heat storage sections 12a and 12b packed with heat storage materials 11a and 11b and combustion gas devices 13a and 13b, water is supplied to one heat storage combustion chamber in which the heat storage materials are heated to obtain steam. The steam is supplied to a treating vessel 20, into which the contaminants containing the volatile materials are supplied, to liberate organic materials from the contaminants. The contaminants are separated to the organic materials O and the water W in a separator 22, and the separated organic materials are introduced into the other heat storage combustion chambers and are burned. The waste combustion gas is brought into direct contact with the heat storage material in the heat storage section and is cooled by a heat exchange and is then discharged. The above operations are alternately carried out in the two heat storage combustion chambers.