Abstract: The molten salt used as an electrolyte of a molten salt battery is a mixed salt between a salt in which the anion is an ion represented by [R1-SO2—N—SO2—R2]— such as FSA ion and the cation is Na ion, and a salt in which the cation is an alkali metal ion other than Na ion or an alkaline earth metal ion. The active material of a positive electrode 1 is a metal oxide represented by NaxM1yM21-yO2 (wherein M1 is Fe or Ni, M2 is Mn or Ti, 0<x?1 and 0<y<1). The active material of the positive electrode 1 is, for example, Na2/3Fe1/3Mn2/3O2. The molten salt battery operates at a low temperature, whereby time required for increasing the temperature of the battery to the operation temperature is reduced. The molten salt battery also has improved safety because the electrolyte is nonvolatile and nonflammable.