To sufficiently protect a branched part from direct external force, with respect to piping laid under the ground surface, even when the construction cost is restrained.

A permanent shield tunnel 17 is constructed in a range wherein a drain branch pipe 14 is taken out in parallel to a main pipe 12 from the branched part 13 in a halfway of the main pipe 12 arranged under the ground surface, and a clearance is maintained around thereof. The external force is not directly applied to the branched part 13 even at an earthquake, and thereby danger of a crack or leakage can be reduced. A temporary shield tunnel 18 is constructed on the other part of the main pipe 12, and the temporary shield tunnel 18 is filled with soil after piping execution. Thus, the execution cost can be reduced.