<p>A guiding flue (10) of refractory material is arranged at the exit of the slag exhaust hole (7) of a plasma fusion furnace (1) to guiding exhaust gas (5) in the downstream direction of the flowing slag. The slag which flows down by the sensible heat of the high-temperature exhaust gas, and the vicinity of the exit of the exhaust hole are forcedly heated to make it possible to prevent block of the exhaust hole in the vicinity of the exit due to solidified slag. By tilting a plasma torch (2) toward the exhaust hole (7) when the exhaust hole begins to be clogged, it is possible to prevent the block.</p>
