Nonaqueous electrolyte secondary battery

Provided is a nonaqueous electrolyte secondary battery which can effectively prevent volatilization of electrolyte or moisture from invading the internal of the battery, and in high-temperature environment, battery characteristics would not degrade, the battery maintains sufficient discharge capacity, discharge capacity is high, and has excellent storage characteristics. The battery includes a bottomed cylindrical positive electrode casing, and a negative electrode casing which is fixed to an opening of the positive electrode casing through a gasket. The opening of the positive electrode casing is caulked to the negative electrode casing side to seal an accommodation space. A caulking tip end in the opening of the positive electrode casing is disposed in an inward direction of the negative electrode casing than a tip end of the negative electrode casing. A diameter d of the nonaqueous electrolyte secondary battery is in a range of 4 mm to 12 mm, a height h1 of the nonaqueous electrolyte secondary battery is in a range of 1 mm to 3 mm, a side surface portion of the positive electrode casing is formed in a curved surface shape, a radius of curvature R is set in a range of 0.8 mm to 1.1 mm, and a height h2 of the positive electrode casing is in a range of 65% to 90% with respect to the height h1 of the nonaqueous electrolyte secondary battery.