To provide a stopper for a cutting tool capable of getting a correct depth required in a medical treatment field, even if a few kinds of a cutting tool are available, without preparing a many cutting tools, the stopper for a cutting tool is fitted to a rotary shaft of a cutting tool having the rotary shaft, the stopper includes a locking member which has a through hole contacting to the rotary shaft of the cutting tool, a clamping member which is made of a shape memory material, provided at the inner and/or outer side of the locking member and can deform the locking member by its recovering force, and a cutout part reaching to the through hole from an outer peripheral edge thereof in the longitudinal direction of the rotary shaft.
