To provide a flat nonaqueous electrolyte battery capable of suppressing the corrosion of a positive electrode case when the battery is stored over a long period in the high-temperature environment.

This flat nonaqueous electrolyte battery is provided with a positive electrode and a negative electrode stored in a sealed container having the structure that a metal positive case 1 is sealed by a negative electrode case 8 via a sealing material 9 and a nonaqueous electrolyte stored in the sealed container and containing a fluorine compound. The positive electrode case 1 is applied with marking on the outer face, and at least the position on the inner face corresponding to the marking is covered with a nonaqueous electrolyte-resistant film layer 3.