A molten metal measuring system wherein elements to be measured of molten meal are measured in a predetermined depth area from a metal level of molten metal on which a slag layer exists, and wherein said system comprises a probe which includes a lower end portion having an immersed portion to be immersed in said predetermined depth area, an upper end portion to be extended above said slag layer when the probe is immersed, measuring means provided in said arranged immersion portion for measuring elements to be measured of molten meal, and a metal detection sensor located at a position below an upper end of the predetermined depth area at a distance (Dx), a sub-lance which is connected to the upper end portion of said probe and with which said probe moves downward at a speed and moves up after stopping the downward movement, a drive device for making said sub-lance move up and down, and a control device having drive command means for making said sub-lance move downward, stop moving and move upward by controlling said drive device, characterized in that: said system further comprises a data creation device including stop position determination means which determines, during the downward movement of the probe, a detection time point and a stop time point which comes after passing a downward continuation time period (Tx) (Tx=Dx/V) from said detection time point, and stop signal output means which outputs a stop signal to said drive command means simultaneously with an arrival of a stop time point, and judging means which receives a detection signal from said metal detection sensor and outputs a detection determination signal to said stop position determination means for determining said detection time point; wherein said metal detection sensor includes a circuit which outputs predetermined voltage to said judging means in which the voltage is reduced by reacting to metal in such a manner that the voltage is reduced by reacting to molten slag layer and is further reduced by reacting to molten metal of which voltage reduction constitutes said detection signal, and judging means receives said detection signal from said metal detection sensor and compares the voltage reduction thereof with a predetermined threshold, and said judging means outputs a detection determination signal to said stop position determination means only when the voltage reduction of said detection signal is judged as exceeding said threshold whereby said stop position determination means determines said detection time point, thereby said stop position determination means is constituted to determine said detection time point only when said metal detection sensor reaches to said metal level of molten meal after passing through said slag layer. said system further comprises a data creation device including stop position determination means which determines, during the downward movement of the probe, a detection time point and a stop time point which comes after passing a downward continuation time period (Tx) (Tx=Dx/V) from said detection time point, and stop signal output means which outputs a stop signal to said drive command means simultaneously with an arrival of a stop time point, and judging means which receives a detection signal from said metal detection sensor and outputs a detection determination signal to said stop position determination means for determining said detection time point; wherein said metal detection sensor includes a circuit which outputs predetermined voltage to said judging means in which the voltage is reduced by reacting to metal in such a manner that the voltage is reduced by reacting to molten slag layer and is further reduced by reacting to molten metal of which voltage reduction constitutes said detection signal, and judging means receives said detection signal from said metal detection sensor and compares the voltage reduction thereof with a predetermined threshold, and said judging means outputs a detection determination signal to said stop position determination means only when the voltage reduction of said detection signal is judged as exceeding said threshold whereby said stop position determination means determines said detection time point, thereby said stop position determination means is constituted to determine said detection time point only when said metal detection sensor reaches to said metal level of molten meal after passing through said slag layer.