To provide a stopper enabling to easily and certainly regulate an entering depth of a blade of a drill in a jawbone of a lost tooth part by only inserting and attaching from the blade side of the drill which has a flange Xa projecting at a shank Xb, regardless of a size of a diameter of the blade.The stopper Y is cylindrically formed in its entirety and inserted and attached from a top side of the blade Xc of the drill X which has the flange Xa projecting at the shank Xb. The stopper has a through hole to be penetrated by the blade Xc of the drill X and includes a drill blade entering depth regulating part Ya and a drill holding part Yb. The drill blade entering depth regulating part Ya has a height, regulating an entering depth of the blade Xc of the drill X in the jawbone of the lost tooth part. The drill holding part Yb has a plurality of slits Yba formed along the axial direction of the stopper from an end opposite to the drill blade entering depth regulating part Ya, detachably engages to the flange Xa of the drill X, and holds the drill X by elasticity.
