PURPOSE: To save labor for construction and to shorten a construction period by installing a joining plate to join a a beam of S structure on a girder of RC structure and joining the beam on the joining plate.

CONSTITUTION: A formwork for a pillar and a formwork for a girder to construct the pillar and a girder 2 are assembled and simultaneously supported by timbering. Thereafter, between the formworks for the girders, a beam 3 of S structure is suspended and its both ends are supported by the timbering of the formworks for the girders. Thereafter, on the beam joint part of the formwork for the girder, a joining plate 4 is installed, and on a coupling part 4a of the joining plate 4, the end part of the beam 3 is joined by a joining bolt 8. Between the beam 3, a deck plate 6 is laid, and in the formwork for the girder and on the deck plat 6, reinforcing steel of the girders 2 and a floor slab 5 is arranged. Additionally, on the formwork for the girder and the deck plate 6, concrete is deposited and cured.