An ending target position Xes corresponding to the measurement ending position Xe, a rotation rate pattern Ar to rotate a screw 2 , and a hypothetical retraction rate pattern Ab for the screw 2 to retract are set in advance, the remaining rotation rate pattern Ar to stop the screw 2 rotation at the ending target position Xes is predicated by calculation based on the screw position X detected at every specified time interval Ts at the time of measurement, based on which the screw 2 is controlled to rotate to the measurement ending position Xe, the remaining retraction rate pattern Ab to stop the screw 2 retraction at the ending target position Xe based on the screw 2 retraction rate Vd detected at every specified time interval Ts, based on which the screw 2 is controlled to retract to the measurement ending position Xe, the rotation and retraction of the screw 2 are stopped, and subsequently the screw 2 is controlled to reverse rotate by a pre-set constant amount of rotation Rc while position controlling its position to the measurement ending position Xe.