a screw 12 for an extruder 10 rotatably supported on the cylinder of the extruder and carrying roll - heated rubber material supplied from a hopper port 13 s provided at the rear part of the cylinder 11 , wherein the height of the portion of the flight portion 12 z of the screw 12 located below the hopper port 13 s is set lower than the height of the flight portion 12 a on the downstream side of the screw 12 , whereby the pulsation of extruded matter can be reduced while maintaining a high discharge rate .