Abstract: A metal melt is used as a measuring electrode while a pure form of a particular metal component to be measured or an alloy containing it is used as a standard electrode. The active substance to come in contact with the standard electrode includes at least one halide of an alkali halide and an alkaline earth halide, both having ion conductivity, and a halide of the particular metal component, any one of such halides consisting of a solid phase and a liquid phase. This active substance is provided such that it can come into contact with the metal melt and is used as an electrolyte as well. It is thus possible to provide a continuous detection of the concentration of the particular component in the molten metal to be measured.