PURPOSE: To realize a high speed fitting work by fitting and fixing a fireproof rock wool forming material to an iron pipe, with hollow tube parts remaining and fitting and combining a pair of separate circular soft piece bodies with the size to fit to the inner size of the hollow tube parts, to the hollow tube parts.

CONSTITUTION: To the inside of an iron pipe 1 larger S1 than a specific size S, a fireproof rock wool plastic material 6 shorter than the iron pipe 1, in which small round holes 3 and 3' responding to penetrating coolant tubes R and R' of an air-conditioning device are penetrated, is fitted and fixed remaining hollow tube parts 7 and 7' at both ends of the iron pipe 1. To the hollow tube parts 7 and 7', a pair of circular soft piece bodies 12 and 12' are fitted. In the circular soft piece bodies 12 and 12', cut holes 10 and 10', and, 11 and 11' with the diameter to fit closely to the ends of warmth keeping tubes 8 and 8' which cover the coolant tubes R and R' by opening and closing in forked directions are provided. As a result, transport, handling, and execution of work are easy, and there is no fear of generating any breakage.