To solve the problems wherein a tool is damaged in processing as a result of a superhard abrasive grain being torn off from the central vicinity of a tip part, and a part of a workpiece contacting with an inner hole can not be processed since the inner hole exists in the center of a rotary shaft, when grinding chips of a ceramic sintered body being the workpiece stagnate in the center of the tip part, in a conventional boring tool.

A columnar rotary body 12 is formed by fixing abrasive grains to the tip part 18, and has: an inner hole 24 opening on a tip surface of the tip part on the inside of the columnar rotary body; and a recessed part extending up to an outer peripheral edge part in one direction by including the rotational center of the tip surface by looking at the tip surface in a plan view in the tip surface of the columnar rotary body.