A longitudinal position word L is encoded with error correction capability. After inserting the probe head between the upper and lower dovetails of the z stage, handles of the pushdown screws are turned so that the lower portion of the upper dovetail rail clamp down the probe head. It is possible to operate the two function blocks using a common BIAS current and additionally to save components. The currents flowing in the corresponding bit lines are amplified with sense amplifier circuits to drive local match lines.