PURPOSE:To produce a mold for forming synthetic resin product in a short period of low cost by a method in which when the forming mold for foamable thermoplastic resin is to be produced, a thin film made by metal-spray is formed on the surface of the mold corresponding to the surface of a formed product, and further reinforcement-layer such as FRP is formed on the outer side of said thin film. CONSTITUTION:Thin film A, A' are formed on both surface of a removable mold 1 by spraying metal such as Al. Next, reinforcement-layers B made of FRP are formed on these thin films A, A'. After they are hardened, the removable mold is removed. Then, steam injection holes C, C' and a raw material filling hole D are bored. After the particles of the foamable thermoplastic resin such as polystyrene are injected into the hole D for filling raw material, and said hole is closed by a stopper. Thus, the resin is heat-formed by a autoclave, and the foamed product is obtained.
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