Abstract: A screw conveyor type delivering and mixing device is for combinational use on a plastics injection molding machine. The screw conveyor type delivering and mixing device comprises a large central screw rod and two small side screw rods that are housed in a delivering tube having a material feeding opening at one end. The delivering tube has a large central tubular portion for accommodation of the large central screw rod and two small tubular side portions for housing the two small side screw rods. The central tubular portion communicates with the two tubular side portions along the full axial length thereof. All the screw rods have sections alternatively having coarse threads, fine threads and medium threads consecutively with different pitches.