A separator (3) of a molten salt battery is impregnated with a molten salt that serves as an electrolyte. The molten salt contains, as cations, at least one kind of ions selected from among quaternary ammonium ions, imidazolium ions, imidazolinium ions, pyridinium ions, pyrrolidinium ions, piperidinium ions, morpholinium ions, phosphonium ions, piperazinium ions and sulfonium ions in addition to sodium ions. These cations do not have adverse effects on a positive electrode (1). In addition, the melting point of the molten salt, which contains sodium ions and the above-mentioned cations, is significantly lower than the operating temperature of sodium-sulfur batteries, said operating temperature being 280-360 DEG C. Consequently, the molten salt battery is capable of operating at lower temperatures than sodium-sulfur batteries.