To provide a supporting plate, the carrying and stacking of which can be easily realized and with which no warpage develops in a hydraulic inorganic molding even when the shape of the matter is a flat plate by a method wherein the thickness of the supporting plate itself is made to be thin.

This supporting plate A of hydraulic inorganic molding is used for curing and hardening the hydraulic inorganic molding. On the rear surface of supporting plate main body 1, on which the hydraulic inorganic molding is placed, a supporting plate reinforcing plate 2, in which crest parts 21 and trough parts 22 are formed, is mounted so as to abut the top surfaces of the mountain parts 21 of the supporting plate reinforcing plate 2 against the rear surface of the supporting plate main body 1.