Reducing fiber breakage and improving fiber dispersion are the most important issue of FRTP in injection molding. The purpose of this study is to suggest an effective screw design for improving both residual fiber length and fiber dispersion. The factors that improve residual fiber length and fiber dispersion were investigated through the molded specimens by different design screws. We found that the screw design in the compression zone dominantly affected the residual fiber length, and that the choice of an appropriate design for the melting and mixing processes was the most important factor for improving both fiber dispersion and residual fiber length. Our experimental observations were compared with the results of flow analysis and consistency was observed. However, flow state of thermoplastic molten resin in heat barrel was not accessible to direct observation. So, we provided a device for visually confirming the flow state in barrel at a glance. As a result, we were able to grasp flow state of the resin in the barrel by using this visualization device and those made further optimization of screw design possible.