A method of forming, on a strip-shaped laminate of multiple reinforcing fiber sheets superimposed one upon another, two flexures with respect to the cross-section configuration thereof, wherein in the forming of the two flexures with the use of two flexure forming dies independent from each other, respectively, the two flexure forming dies are arranged so that the relative distance of the two flexure forming dies is changeable in the direction perpendicular to the longitudinal direction of the strip-shaped laminate. This method can be effectively utilized in the production of a reinforcing fiber molding with changing of the distance between the two flexures namely, width of web portion or gauge between two flange portions from the strip-shaped laminate, or the production of fiber reinforced resin (FRP) molding therefrom.