To provide the forming device of hydraulic inorganic formed matter, which has a uniform specific gravity and strength and, needless to say, with which a dense and high strength formed matter can be obtained without making the structure of the forming device more complicated.

In the forming device 1a, in which a hydraulic inorganic forming material is forced in a cavity formed by closing a top and a bottom molds 2 and 3 together and then shaped in the desired shape by vacuum-dehydrating the excess water content in the hydraulic inorganic forming material through drainage holes 21 bored on the molding surface of the bottom mold 2, by changing the thicknesses of a portion 51 abutting against the lower edge face 31a of the projecting part 31 of the top mold 3 and of a portion 52 abutting against its projecting part 31b of an elastic sheet 5, the pressures applying to the hydraulic inorganic forming material are made equal to each other.