To obtain a molding having excellent surface smoothness of a hollow part and no abnormal irregular thickness part by forming it of additive and thermoplastic resin, and using a granular material having a high additive- containing content part and no or small additive-containing content part.

As additive and thermoplastic resin for constituting granular material, glass fiber and MXD6 nylon are used. The nylon is supplied from an upstream side of a biaxial extruder, melted and kneaded. At this time, it is strongly kneaded. And, the fiber is supplied by a side feeding process at an intermediate flow of the extruder, and molten thermoplastic resin and the additive are kneaded. At this time, it is kneaded by an intermediate degree. Further, the nylon is supplied based on a side feeding process at a downstream side of the extruder, and the molten resin and the kneaded material are kneaded. At this time, it is weakly kneaded. Eventually, strands discharged from the extruder are cut in a desired length to granulated material.