An apparatus having a kneading part for performing kneading of a material and an injecting part for performing injection of the material in an injection molding operation with the kneaded material. The kneading part and the injecting part are connected together. The injecting part includes a weighing screw channel portion for weighing the material and a retention screw channel portion that is formed adjacently to the weighing screw channel portion. The injecting part has an injection screw shaft defining differently shaped channels that form a material retention space for retaining the material fed continuously quantitatively from the kneading part. Thereby, the material fed continuously quantitatively from the kneading part can be securely retained in the injecting part where intermittent operation is performed.