To provide a ring reducer capable of positioning the ring reducer itself concentrically to a fixation hole by preventing a portion from running on to a peripheral wall of the fixation hole to float even when the hole diameter of the fixation hole is smaller than a circle connecting outer circumferential side tip parts of respective positioning protrusions due to dimensional tolerance of the fixation hole.

A ring reducer used to fix a splicer having a diameter smaller than an inner diameter of a fixation hole 32 to the fixation hole 32 formed to fix the splicer for connecting a tube includes a reducer body 11 formed in the shape of a plate having a circular hole 12 having a diameter corresponding to the splicer having a small diameter in the center. The reducer boy 11 includes positioning protrusions 21 inserted into the fixation hole 32 to be engaged with an inner surface of the fixation hole 32 to position the circular hole 12 with respect to the fixation hole 32, and the positioning protrusions 21 are formed in an elastically deformable manner.