To provide a fire-proof skeleton penetrating drain pipe unit which simplifies works by dispensing with the assembling works at a construction site and improving the workability, and to provide its construction method.

Connecting drain pipes 3 and 6 of upper/lower floors S1 and S2 partitioned by a floor slab 1, or a fire-proof skeleton are connected to a non-fireproof drain pipe 12 of a unit 20 inserted in a through-hole 2 of the floor slab 1 via joints 4 and 5. The unit 20 is formed of a case 11, the drain pipe 12 inside the case 11, a fire-proof thermal expansion material 13 disposed between the case 11 and the drain pipe 12 and closing the drain pipe 12 and the through-hole 2 expanded and dissolved in occurrence of a fire, and mortars 14 and 15 disposed in the both sides of the thermal expansion material 13 in the axial direction of the drain pipe 12. These are connected and integrated at factory beforehand, and are carried to the construction site.