PURPOSE:To enable to ingition of a gas burner to be rapidly performed, and enable discharge of a fuel gas to be reduced by connecting an ignition-fuel-gas introducing path to a communicating path, which is connected to a gas path, after the end of the former process so as to store the ignition-fuel-gas in the gas path until the next process is started. CONSTITUTION:The seal-off process of an exhaust tube 9 is composed of preheating, seal-off heating, so called burr cut and stress removal which are continuously carried out in that order. After the seal-off process is finished, a chipping burner is extinguished. Next, a movable-side communicating path 15 is connected to an ignition-fuel-gas introducing path so as to supply an ignitio fuel gas to the chipping burner 10 through the ignition-fuel-gas introducing path. Here, time during which the movable-side communicating path 15 and the ignition-fuel- gas introducing path are connected to one another is set so that a seal-off gas path 16 can be alsmost filled with the ignition fuel gas. Thus, after the end of the seal-off process, the ignition fuel gas is stored in the seal-off gas path 16.
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