To simply and surely install a fitting pipe on an existing pipe by previously fixing a fitting pipe water-tightly and firmly to an existing pipe and easily and surely boring a through hole.

A sheath pipe 3 is installed between an existing pipe 1 or the like and the ground surface side, after sediment in the sheath pipe 3 is discharged to the ground surface side, the interior of the sheath pipe 3 is cleaned, a fitting pipe coupling 4 having a fitting seat part 6 is provided on the lower end of a short cylindrical part 5, and the fitting pipe 2 where the fitting pipe coupling 4 is fixed to the forward end part thereof is inserted in the sheath pipe 3. After the fitting pipe is fixed water-tightly and firmly to the fitting position of the existing pipe 1, a boring and circular cut piece recovering device 10 is inserted in the fitting pipe, the existing pipe 1 is bored by a central boring bit 12, and a recovering click 11 is expanded in the inside of the existing pipe 1. A through hole 14 is bored in the existing pipe 1 by a circular bit 13 and a circular cut piece 15 cut off by the above boring is hooked and held on the recovering click 11 and recovered together with the device 10 to the ground surface side to install the fitting pipe 2 to the existing pipe 1 or the like.