To construct an RC slab with excellent economical efficiency by enabling raising of the RC slab without the need for a raising material.

In a structure of this flat deck plate 1 with a closed end, the closed ends 1a in a position below an undersurface of a rib, which are constituted by crushing a flat plate 2 to a position lower than the undersurface position of the stiffening rib, are formed at both the longitudinal ends of the flat deck plate which is equipped with the plurality of stiffening ribs formed by bending the flat plate on a top surface downward over a length direction, respectively. When the RC slab 15 is constructed using a permanent form in which the closed ends 1a of both the longitudinal ends of the flat deck plate 1 with the closed end are placed on a beam 6, the RC slab 15, which is raised in such a manner that the undersurface position of the stiffening rib is higher than the top surface of the beam 6, is obtained. The raised RC slab 15 can be constructed at a raising height most suitable for each individual object without the need for the raising material; and an excessive design, in which the slab thickness d of the RC slab 15 is excessively increased, can be avoided.