PURPOSE: To readily and rapidly add an alkali solution, by blending the alkali solution at one or plural positions within a transfer region of a process for kneading, extruding and forming a food material while transferring the food material under pressure.

CONSTITUTION: A food material is fed into a cylinder 11 of an extruder 10 by a feeding device 20 for the food material. An alkali solution is fed from a solution supply hole 31 by a pump 33 of a solution supply means 30 and blended with the food material. If the solution supply hole 31 is provided in each of the initial stage part (31a), intermediate stage part (31b) and kneading end part (31c) of a kneading process within the transfer range, the feed rates to such parts are respectively and separately adjusted, as necessary.