PURPOSE: To eliminate intermetallic contact in a nozzle and to enable high temp. operation by providing a fixed part and a telescoping part to the nozzle and providing an outer feedback air channel sliding along the periphery of an inner feedback air channel to the telescoping part, and providing an outer extension part sliding along the periphery of a side channel thereto.

CONSTITUTION: A nozzle 10 has the side channels 6, 6' of a pair of slot nozzles and the feedback air channel 5 arranged at the almost center of the nozzle 10 has upper flanges 21, 22 receiving a upper support 100. A nozzle gap is prescribed by a slot plate 3 and the side channels 6, 6' and fixed gaps 30, 30' are formed. The slide outer feedback air channel 12 connected to the slide outer extension parts 16, 16' in the telescoping part of the nozzle 10 is fitted to the periphery of the feedback air channel 5 in a slidable manner. The slots 30, 30' receive the side slot nozzles 6, 6' in a slidable manner and air is discharged trough these slots.