To provide a rubber extruder capable of efficiently removing volatile components in unvulcanized rubber without decreasing productivity of the unvulcanized rubber. The rubber extruder 1 is for extruding the unvulcanized rubber (G) while kneading. It includes a barrel 2 having an input port 5 for introducing the unvulcanized rubber (G) and a discharge port 6 for discharging the unvulcanized rubber (G), a screw 3, which is arranged in the barrel 2, for extruding the unvulcanized rubber (G), and a vent 4 for sucking out air in the barrel 2. The screw 3 has a dam portion 7 which locally controls an extrusion amount of the unvulcanized rubber (G), a first screw portion 8 defined between the input port 5 and the dam portion 7, and a second screw portion 9 defined between the dam portion 7 and the discharge port 6. An effective screw length (L1) of the first screw portion 8 is 50% or more of a total effective screw length (L) of the screw 3.