A rolling member fitted into a guide recess and capable of performing a wedge action on a collar of a rotary quill is held by an annular holder in such a manner that the longitudinal movement of the rolling member can be restricted and the outside of the annular holder is rotatably fitted with an annular outer frame for restricting the outward movement of the rolling member, thereby forming a brake main body. By rotating the annular holder by use of a rotation operation member provided in the annular holder, the rolling member is controlled such that it can be restricted and held at an operative position allowing the wedge action or at a non-operative position prohibiting the wedge action, thereby switching the rotary quill to a reversal preventive position or to a reversal allowable position. Also, the brake main body is constructed as detachable one unit.
