PURPOSE: To improve the treatment of organic substances in a method in which the organic substances fermented or dried in a treatment vessel can be extruded efficiently and continuously from a discharge opening without being affected by the properties and back pressure of the organic substances.

CONSTITUTION: A cylinder 23 is installed in a treatment vessel 1 equipped with a mixing screw 10, and the first carrier screw 21, which has the same shaft condition as the mixing screw 10, and the second carrier screw, which is engaged with the first screw 21 in parallel, are arranged. The discharge opening side of the treatment vessel 1 is made in a conical form, the diameter of which decreases toward the first carrier screw 21, and the periphery of the mixing screw 10 is made in a conical form along the conical wall face 1e of the treatment vessel 1. The thread of the first carrier screw 21 is extended to expand along the conical wall face 1e of the treatment vessel 1, and the phase and direction of the thread are made the same as those of the mixing screw 10.