The present invention provides an extruder configured to extrude a solid raw material containing moisture, the extruder comprising: a barrel having a hollow tubular shape in a longitudinal direction, wherein a hopper into which a raw material is put is coupled to one side of the barrel, a discharge port through which a dehydrated raw material is discharged is provided on the other side of the barrel, and a slot portion, through which the inside and outside of the barrel communicate each other, is provided in a specific section between the discharge port and the hopper; a rod-shaped screw provided with screw threads on an outer circumferential surface thereof so that the screw is mounted within the barrel to transfer a raw material put into the hopper to the discharge port while axially rotating in one direction; and a heater part mounted on the barrel to heat the raw material. The raw material introduced into the barrel through the hopper is gradually heated by the heater part while being transferred within the barrel through the screw. A kneading zone, in which raw materials transferred by the screw threads are compressed, is formed on the screw. Since the raw material is melted within the barrel so that at least a portion of the raw material is phase-changed into a liquid state, a heating temperature of the heater part and an axial rotation speed of the screw are controlled so that a sealing membrane that shields an inner transverse section of the barrel is formed from the liquid raw material in the kneading zone.