To provide a molten salt battery which is highly safe and has long charge/discharge cycle life. The molten salt battery of the present invention includes a negative electrode 1 in which a negative electrode active material 12 is predominantly composed of carbon such as hard carbon. The negative electrode active material 12 is surface-treated for imparting hydrophilicity to the negative electrode active material 12 to improve the affinity for the molten salt. Further, a transition metal such as iron is added to the negative electrode active material 12 predominantly composed of hard carbon in order to enhance the affinity for the active material. The molten salt battery has higher safety in production and use and longer charge/discharge cycle life than conventional molten salt batteries using metallic sodium as an electrode.