PURPOSE: To extract a reinforcing steel cage in the state of cutting soil pressure by way of changing an existing cast-in-place pile into a hollow pile and crushing its concrete from the inside by means of diameter expansion and to simultaneously prevent breaking of the ground around an extraction hole of the reinforcing steel cage.

CONSTITUTION: A cast-in-place pile is changed into a hollow pile by forming a cut hole a in the central part of the cast-in-place pile, and peripheral concrete of the cut hole a is expanded in diameter from the inside and crushed 6. A reinforcing steel cage 2 is extracted by cutting soil pressure by way of burying a casing underground in order to surround a crushed concrete structure and engaging a diameter expansion member 5 with the lower part side of the reinforcing steel cage. Thereafter, the casing 12 is extracted after charging backfilling sand C in the extracted hole.