PURPOSE: To form a hole having an uniformly expanded portion by a method in which a shaft having a blade on its periphery is rotatably thrust through the first cylinder eccentrically and supported, and the first cylinder is rotatably thrust through the second cylinder eccentrically.

CONSTITUTION: The second cylinder 13 is penetrated into a hole 22 drilled in a base material 21 (e.g., concrete, rock bed, etc.) under the condition that the cylinder 14 of the second cylinder 13 is matched with a shaft 1 concentrically. The cylinder 13 is set by closely contacting the cylinder 14 with the wall of the hole and also closely contacting the collar 15 with a base material 21. The first cylinder 8 is moved eccentrically little by little by means of a handle while turning the shaft 1 to cut the wall of the hole, where the eccentrical amount is increased when turning the cylinder 8 through 180° and a projection 19 comes to collide with a stopper. When the cylinder 8 is further turned, the cylinder 13 is also turned, the shaft 1 revolves on a circle of a radius of 2e at the center of the hole 22 to cut the wall of the hole 22, and an expanded portion 23 is formed when the cylinder 13 is turned through 360°.