supplied gas is ignited and flame is generated as the plasma generating gas nitrogen air oxygen steam argon or the like may be supplied each gas supply line may be provided with a filter for removing foreign substances within gas a flow controller for controlling the amount of supplied gas and a valve for controlling the gas supply line the plasma generating gas supplied to the hydrogen sulfide and carbonyl sulfide supply chamber 10 may be one kind of gas or a mixture of various kinds of gases further the plasma generating gas may be supplied alone or supplied through a mixed gas supply pipe 12 after being mixed with synthetic gas including hydrogen sulfide and carbonyl sulfide in a mixing device 11 as shown in the drawing herein the mixed gas supply pipe 12 communicated with the hydrogen sulfide and carbonyl sulfide supply chamber 10 may be configured alone otherwise a plurality of the mixed gas supply pipes 12 may be provided at equal intervals according to the circumference of the hydrogen sulfide and carbonyl sulfide supply chamber so that the mixed gas can be supplied through them at once also the mixed gas supply pipe 12 is provided in such a manner that it can be laterally apart from the axial center of the hydrogen sulfide and carbonyl sulfide supply chamber 10 as shown in fig2 and toward the bottom of the hydrogen sulfide and carbonyl sulfide supply chamber 10 as shown in fig3 this allows the supplied mixed gas to be moved as a swirl stream swirling at a high rate on the inner surface of the hydrogen sulfide and carbonyl.