Disclosed is a method for operating a molten salt battery that comprises: a molten salt as an electrolytic solution; a sodium compound (NaCrO2) as a positive electrode; and tin (Sn) as a negative electrode. The operation temperature range of this molten salt battery is normally from 57 DEG C to 190 DEG C. However, by operating this molten salt battery by setting the inner temperature thereof (the temperature of the electrodes and the molten salt) from 98 DEG C to 190 DEG C, the sodium is brought into the liquid phase and penetrates into the Sn-Na alloy that has been reduced to fine particles on the negative electrode. Thus, the detachment of the Sn-Na alloy is inhibited.