To simplify joining work when joining end parts of multicore cable protecting tubes by eliminating the need to peel end parts of outer tubes fixed to inner tubes.

Respective end parts of the outer tubes 18 and the four inner tubes 16 of the multicore cable protecting tubes 12 and 14 are mutually butted, and they are joined in a state with positional relationships of respective end parts of the mutually butted inner tubes 16 fixedly maintained by an inner tube socket 28. Consequently, even when the outer tubes 18 and respective inner tubes 16 are mutually fused by fusion parts 24, the end parts of the protecting tubes 12 and 14 can be joined by inserting the inner tube socket 28 into gaps 26 between the outer tubes 18 and the inner tubes 16.