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 an undersurface position of a rib, which are constituted by crushing a flat plate 2 to 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 2 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 raised with respect to the top surface of the beam 6 is obtained. An excessive design, in which the slab thickness d of the RC slab 15 is excessively increased, can be avoided without the need for the raising material.