The embodiment of the invention discloses a limit adjusting device which comprises a rotator, an adjusting sleeve and a locking mechanism, wherein the adjusting sleeve is sleeved on an adjusted piece and can only move along the axial line of the adjusted piece; one end of the adjusting sleeve is provided with external threads, the rotator is provided with internal threads and sleeved on the adjusting sleeve, and the threads of the adjusting sleeve and the rotator are matched; a drill bit is provided with a limiting device used for limiting the axial line of the rotator to move and an assembling hole used for containing the locking mechanism; the locking mechanism specifically comprises a locking device and an elastic piece, wherein the locking device is arranged at one end of the elastic piece and the locking device and the elastic piece are arranged in the assembling hole; and the rotator is provided with a locking hole which can clamp the locking device. As the limit adjusting device disclosed by the embodiment of the invention is provided with the locking mechanism, when the rotator is rotated and the adjusting sleeve is driven to move, the locking hole of the rotator is rotated to a position close to the locking device, the elastic piece pushes the locking device so that one part of the locking device enters into the locking hole of the rotator for being clamped, furthermore, the adjusting sleeve is locked at the required position for being positioned.