An extruder comprising: a cylinder having a first end portion and a second end portion respectively formed at two ends of the cylinder in an axial direction, and an ejection port formed in the first end portion; a screw including a shaft configured to rotate within the cylinder, and a screw blade provided on an outer circumferential surface of the shaft; a supplier attached to the second end portion side of the cylinder and configured to supply a kneading target to an inside of the cylinder; and a plurality of protruding members protruding from an inner wall surface of the cylinder, wherein an intermediate section of the screw in the axial direction is provided with at least one compressor that is configured to compress the kneading target while the kneading target is being transported, and to cause the kneading target to generate heat, the cylinder is provided with a degassing hole that is located downstream of each compressor and is in communication with an outside of the cylinder, and the compressor includes: a dam part that joins sections of the screw blade that are adjacent in the axial direction; characterized in that the dam part extends in the axial direction; and that the compressor further includes: a plurality of grooves formed along the axial direction in outer circumferential surfaces of the adjacent sections of the screw blade that connect two end portions of the dam part such that the kneading target held back by the dam part is transported downstream in the cylinder via the grooves. a cylinder having a first end portion and a second end portion respectively formed at two ends of the cylinder in an axial direction, and an ejection port formed in the first end portion; a screw including a shaft configured to rotate within the cylinder, and a screw blade provided on an outer circumferential surface of the shaft; a supplier attached to the second end portion side of the cylinder and configured to supply a kneading target to an inside of the cylinder; and a plurality of protruding members protruding from an inner wall surface of the cylinder, wherein an intermediate section of the screw in the axial direction is provided with at least one compressor that is configured to compress the kneading target while the kneading target is being transported, and to cause the kneading target to generate heat, the cylinder is provided with a degassing hole that is located downstream of each compressor and is in communication with an outside of the cylinder, and the compressor includes: a dam part that joins sections of the screw blade that are adjacent in the axial direction; characterized in that the dam part extends in the axial direction; and that the compressor further includes: a plurality of grooves formed along the axial direction in outer circumferential surfaces of the adjacent sections of the screw blade that connect two end portions of the dam part such that the kneading target held back by the dam part is transported downstream in the cylinder via the grooves. a dam part that joins sections of the screw blade that are adjacent in the axial direction; characterized in that the dam part extends in the axial direction; and that the compressor further includes: a plurality of grooves formed along the axial direction in outer circumferential surfaces of the adjacent sections of the screw blade that connect two end portions of the dam part such that the kneading target held back by the dam part is transported downstream in the cylinder via the grooves.