To obtain the same extent of strength with a newly established pipe and to decrease work time and cost by digging only one-side even if a whole existing pipe is not dug out.

A pipe 11 to be internally inserted is inserted into the existing pipe 10 and an outside face of the pipe 11 is expanded at a top end and a base end, and thus the outside faces of the pipe is made adhere with an inside faces of the existing pipe 10. The expanding pipe 11 is carried out by installing a retainer 12 around an inside part thereof and force-fitting a pons (expanding jig) 16 with a pressing cylinder 15. The pressing cylinder 15 is held by a thread part 13 formed on the periphery at a base end side of the pipe 11, so that reactive force at the time of press fitting is received by the interpolation pipe 11 itself.