To form a straight excavated hole in ground by preventing a deviation of a load and a deflection of a main shaft of excavation during the excavation of the ground.

In an excavating tool 13, a casing 10 is externally fitted and mounted on the outer peripheral surface of the rotatively-driven main shaft 9 of excavation; a sheet pile P is arranged and supported on the outer peripheral surface of the casing 10; and a leading end of the main shaft 9 is equipped with a bit portion 15 which is evenly diameter-enlarged on the axis line O of the main shaft 9 by excavation resistance from the ground G when the main shaft 9 is rotated in the direction of excavation, and which is diameter-reduced to a size small enough not to collide with the sheet pile P, by frictional resistance to the ground G, when the main shaft 9 is rotated in a direction opposite to the direction. Excavation equipment 1 for use is fitted with the excavating tool 13 via a down-the-hole hammer 12. The excavation equipment 1 is supported in a rising attitude; the casing 10 and the sheet pile P are jacked while the ground G is excavated by the bit portion 15 of the excavating tool 13 rotatively hit in this state; after the completion of the jacking of the sheet pile P, the bit portion 15 of the excavating tool 13 is put into a diameter-reduced state; and the excavating tool 13 and the like are pulled out from the ground G.