PURPOSE: To improve the extent of workability in the case of branch piping by installing a double branch part, connecting another pipeline to another side, in a header body partitioned off into two chambers with another connection and one side of two chambers installed in this header body and one side pipeline of a double tube.

CONSTITUTION: In a header coupling 10, an inner part of an almost hollow cylindrical header body 12 is bisected by a partition wall 14 into an upper chamber 16 and a lower chamber 18. Each left end of these chambers 16 and 18 is provided with connections (tapped holes) 24 and 26 for connecting each of main tubes 20 and 22. Two branch parts 28 are formed in a lower part of the chamber 18 at a specified interval. A coupling 42 for connecting a double tube 40 consisting of an inner tube 36 and an outer tube 38 is attached to this branch part 18. In consequence, when branch piping takes place from these two main tubes, it can be done by one header coupling alone and, what is more, this branch piping can be done by the double tube.