PURPOSE: To secure water gradient by lowering the position of the annexed beam of an upstairs outdoor floor suspending channel body for receiving the floor panel where an upstairs outdoor floor ranging to an external wall than that of a main body floor beam, and inclining a joint beam with the annexed beam side down.

CONSTITUTION: An upstairs outdoor suspending channel body 7 is composed of a main body floor beam 3, which receives the external wall panel 2 for formation of an upstairs external wall W, an annexed floor beam 4, which is arranged parallel with this and apart from the external wall W, a joint beam 5, which joins the main floor beam 3 with the annexed floor beam 4, and a receiving beam 6, and it receives the floor panel 10 of an upstairs outdoor floor 9 ranging to the external wall W. Moreover, the joint beam 5 and the seat plate 34 on the outdoor side are applied to the lattice 29 of the annexed floor beam 4, and the upside is lowered by the amount of the thickness of the floor panel 9 from the upside of the floor beam 4. Furthermore, the seat plate 34 on the indoor side of the joint beam 5 is applied to the lattice 17 of the main body beam 3, and the joint beam 5 is inclined with the annexed floor beam 4 side down. Hereby, with the security of water gradient, the rooftop outdoor floor can be diversified.