PURPOSE: To chamfer easily the end of a hole bored on a member with a cutting edge made of the sharp angle part on the opening circumference of the hole by a method wherein a sphere is fixed solidly with the end of a rotary shaft and a hole is bored to the sphere on the slant to the axis of rotation.

CONSTITUTION: A hole 3 is bored on a sphere 2 formed solidly with the end of the shaft 1 of rotation to form cutting edges 4, 5. The hole 3 is provided with a certain angle or on the slant to the axis 1 of rotation. Said sphere 2 is located in contact with the end 13 of a hole 12 made on the member 11. When the shaft 1 of rotation is revolved in an arrow direction, the cutting edges 4, 5 of the hole 3 are pressed on the end 13 of the round hole 12 to chamfer the end.