PURPOSE: To make it possible to precisely insert a reamer in a predrilled hole, concentrically therewith, so that the accuracy of a dimension between axes of holes may be enhanced without the necessity of skill and jigs, by forming, at the tip end of a reamer body, a guide part having a diameter substantially equal to the inner diameter of a predrilled hole in an article.

CONSTITUTION: Blades 2 having a saw tooth shape are formed in the outer surface of a reamer body 1 as longitudinal line grooves, and the outer diameter of the reamer body 1 at the edges of the blades 2 is made equal to the finishing dimension of a hole in an article. At the tip end of the body 1, a guide part 3 concentrical with the body 1 is formed, having a small diameter so that the guide part 3 forms a stepped part having a suitable length. Saw-like blades 4 similar to the blades 2 of the body 1 are formed in the guide part 3, having a diameter equal to that of the predrilled hole at the edges of the blades 4, and cutting blade tips 5 having a predetermined cutting angle and a relief angle are formed in the stepped end face at the boundary with the body 1. Thus, the reamer may be precisely inserted in the predrilled hole, concentrically therewith, due to the guide function by the guide section and the predrilled hole.