To prevent chipping of a drill blade and to allow a drill positioning ring to be inserted to the drill having larger diameter than that of a holder.

An attaching device 1 of the drill positioning ring is used for attaching the drill positioning ring 4 to the drill 2 and includes a drill setting part 8, a ring arranging part 13 for arranging the drill positioning ring 4, a moving unit 20 for moving the drill 2 toward the drill positioning ring 4 arranged by the ring arranging part 13. The drill 2 is set by the drill setting part 8 so that a holder 3 is positioned on a side facing the ring arranging part 13. The moving unit 20 holds the holder 3 and relatively moves so as to face the drill positioning ring 4. Thus the drill 2 is forcibly inserted to the drill positioning ring 4 from a side of the holder 3.