PURPOSE: To easily remove the head of a pile by a method in which a liquid separating agent is injected with stirring into an extra-banking concrete higher than the base finish face of a concrete foundation pile in such a way as to separate gravel, sand, and cement in the extra-banking concrete and thereby to weaken their coagulating forces.

CONSTITUTION: Concrete for a foundation pile 1 is placed to a concrete finish face 5, and immediately thereafter a separator consisting of a shaft pipe 7, a separating blade 8, and a jet pipe 9 is thrust into an extra-banking concrete 3 from the concrete finish face 5 to a base finish face 2 while being turned. The separator is moved in the vertical direction 11 within the range of extra banking dimension 4 and at the same time a separating liquid 12 by which the coagulation of concrete is interrupted is injected 14 and 15 into the extra-banking concrete 3 from a jet pipe 9 in such a way as to separate the gravel, cement, and sand of the extra-banking concrete 3 and thereby to weaken their coagulation forces.