Abstract: A sub-lance assembly for sampling and temperature-measuring of molten metal during refining in a top-blowing oxygen converter, which comprises: a sub-lance having a concentric three-pipe structure comprising from inside to outside an air supply pipe, a water discharge pipe and a water supply pipe; a water supply outer cylinder having a water supply branch pipe, rotatably engaging with the upper end portion of said water supply pipe; a water discharge outer cylinder having a water discharge branch pipe, rotatably engaging with the upper end portion of said water discharge pipe; said water supply branch pipe and said water discharge branch pipe being integrally connected together by a fixing plate; a drive mechanism fitted onto the outer surface of said water supply outer cylinder or said water discharge outer cylinder, for rotating said sub-lance around the axial line thereof; and a sub-lance rotation angle detector at the tip of the axis of rotation of said drive mechanism, for detecting the angle of rotation