NOVELTY - A combustible waste material is gasified in thermal decomposition furnace (2). Decomposition gas is reacted with oxygen and steam and reformed. Reformed gas is introduced into syngas cooler (14), and cooled at preset condition. The condensation-collected material of syngas cooler (14) is ejected. Moisture content is separated from the condensation-collected material. Obtained flammables is returned to thermal decomposition furnace, decomposed and gasified, or supplied as heat source to thermal decomposition furnace. Thus, the gasification gas is purified.    USE - For purifying gasification gas of waste material such as waste tire and waste plastic.    ADVANTAGE - The method enables economical purification of gasification gas, without environmental pollution by organic halogen compounds such as heavy metal and dioxin contained in char and tar.    DETAILED DESCRIPTION - A combustible waste material is gasified in a thermal decomposition furnace. The thermal decomposition gas is made to react with oxygen and steam in a reformer (13), and reformed. The reformed gas is introduced into syngas cooler (14), and cooled to 90-70degreesC less than adiabatic saturation temperature, by water spraying or submerged combustion. The dioxin concentration of the obtained gas is made into less than reference value (0.1 ng-TEQ/m3 N (12% of oxygen concentration reduced value)). The coke oven gas line is made to join an iron mill by dry main (23) which accompanies the existing coke oven (22) and purified. The condensation-collected material of syngas cooler (I) is ejected. Moisture content is separated from the condensation-collected material. The obtained flammables such as char, tar and light oil is returned as fuel to a thermal decomposition furnace, again thermally decomposed and gasified, or supplied as a heat source to a thermal decomposition furnace.    An INDEPENDENT CLAIM is included for refiner of gasification gas.    DESCRIPTION OF DRAWING(S) - The figure shows the block diagram of refiner of gasification gas. (Drawing includes non-English language text)    Thermal decomposition furnace (2)    Combustion furnaces (3,16)    Heat exchanger (4)    Reformer (13)    Syngas coolers (14,17)    Electrostatic precipitator (18)    Gas exhauster (19)    Gas heater (20)    Activator-carbon filled layer or activator-carbon moving bed (21)    Coke oven (22)    Dry main (23)