PURPOSE:To simplify largely a manufacturing process for a mold and to rationalize an apparatus, by preparing a fiber reinforced plastic (FRP) mold based on a clay model or an extended model and by fitting the FRP mold on a metal block which is to become a mold. CONSTITUTION:A clay model 1 or an extended model is prepared (A). A releasing agent 2 is coated on the surface of this model (B). A layer of a FRP 3 is formed on the surface of the model 1 by spraying the uncured FRP 3 from a nozzle on the surface of the model 1. The uncured FRP is then cured and the cured FRP is thereafter taken off from the model (C). The surface of this FRP mold 4 is treated by such a treating device 5 as a sander, etc. On the other hand, a metal block 6 and a male mold 7 are provided separately (D). The above described FRP mold 4 is fitted in a cavity 8 formed in the metal block 6 and fixed with bolts etc. to complete a female mold 10. The manufacturing process for the mold can be thereby largely simplified and both the shortening of the manufacturing time and the rationalization of the apparatus can be achieved.