PURPOSE: To improve the degree of crushing and kneading, and to carry out the sufficient treatment of the titled material at high temperature and pressure, by using a cylinder containing plural screws each having a round kneading zone at the charging side, a trapezoid heating zone, and a square compression zone.

CONSTITUTION: The high-proteinous material charged from the hopper 2 is transferred through the connection zone 3 into the cylinder 4, and sent forward by the rotation of plural screws 5 fixed to a spline shaft. The material is kneaded in the kneading zone 9 having spiral round groove 6 with water or hot water supplied from the liquid feed pipe 12, and then heated with the temperature-controlling pipe 14 in the heating zone 10 having spiral trapezoid groove 7. The processed material is introduced into the compression zone 11 having spiral square groove 8 to effect sufficient compression, and extruded through the orifice 16 into the atmosphere to expand the material. Even a material having high protein content can be sufficiently expanded.