To provide an underfloor piping extremely facilitated its laying and fixing works and prevented from obstructing other works.

A piping unit 10 provided with a prescribed-length major pipe 20 formed of a flexible pipe and prescribed-length branch pipes 30 formed of a flexible pipe and having the major pipe 20 connected to the branch pipes via branch parts 40 is arranged in a prescribed position in the underfloor ground. Fixing weights 60 are placed in appropriate positions in the piping unit 10 so as to fix the major pipe 20 and the branch pipes 30 to the ground.