Abstract: A knockout tool for joint prostheses has a curved tool head, which has a passage for receiving a prosthesis shaft and has a locking device which releasably blocks the prosthesis shaft in the passage, characterized in that the locking device has a blocking element engaging the passage, whose engagement position is adjustable for the sake of adaptation to various prosthesis shaft diameters, wherein an adjusting force, serving to adjust the engagement position and acting upon the blocking member, is transmitted along the curved tool head.