PURPOSE: To exactly form a pile under the ground by a method in which the ground is excavated by an auger head detachably attached to a casing, the auger head is pulled up, an iron bar cage is inserted into the casing, and ready- mixed concrete is placed.

CONSTITUTION: An auger head 2 is fixed by locking to the tip of a casing 1, a hanging rope 23 is attached to the upper fitting cover 4, and the ground is vertically excavated by the auger head 2 while turning the casing 1. The locking of the auger head 2 to the casing 1 is released and the auger head 2 is pulled up to the ground's surface. An iron bar cage 24 is inserted into the casing 1, ready- mixed concrete 25 is placed, and the casing 1 is pulled up to the ground's surface while being turned reversely to form an underground pile 26.