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Redox reaction of platinum ion in 50 PbO・50 SiO_2 (molar ratio) melt was analyzed electrochemically using cyclic voltammetry and chronopotentiometry. The platinum ion in the melt was reduced at around -250 mV (Pt^<2+>/Pt^0), in the temperature range 800℃-1000℃. From the results of cyclic voltammogram, it is suggested that in the system of 50 PbO・50 SiO_2 dissolving Pt, the reaction rate of reduction of Pt ion is much higher than that of oxidation and the rate of electron transfer at electrode surface is slower than ion diffusion. It was found that the electron transfer number of platinum ion is 2, meaning that platinum ion is dissolved as Pt^<2+> and the reaction on the electrode is Pt^<2+>+2e^-→Pt^0. Various parameters such as the diffusion coefficient and the reaction rate were determined for the melt in which high concentration of platinum was disolved.