PURPOSE: To prevent the collapse of excavated pits by a method in which arm levers having a trowel face are provided to the middle of a rotary shaft having an excavating blade on its tip, and during the excavation, excavated soil is sludged by the arm levers and the wall face of the excavated hole is reinforced by the trowel face.

CONSTITUTION: When penetrating a rotary shaft 10 having arm levers 19 with a trowel face 20 on its intermediate portion and a fixed excavating blade 12 on its tip into the ground while being turned, the soil excavated by the blade 12 is adhered to the wall of an excavated hole D by the trowel face 16 of an expandible blade 14 folded and the trowel face 20 of the arm lever 19, and thereby the wall of the hole D is reinforced. When reversely turning the shaft 10, the blade 12 is expanded to form an expanded hole portion F. Cement milk A is discharged from a nozzle 11 at the tip of the rotary shaft, and the sludgy soil in the hole D is replaced with cement milk A to construct a cast-in-place pile.