A sealed battery comprising: an electrode body that forms a positive electrode and a negative electrode; an electrolyte; and a sealed case that houses the electrode body and the electrolyte, wherein a safety valve (40; 140; 240; 340) that opens when internal pressure of the case rises to equal to or greater than a predetermined value is formed in a portion of the case; wherein the safety valve (40; 140; 240; 340) includes a thin portion (42; 142; 242; 342) formed thinner than the surrounding portion of the safety valve (40; 140; 240; 340), and a fracture groove portion (50; 150; 250; 350) formed in the thin portion (42; 142; 242; 342); wherein the thin portion (42; 142; 242; 342) differs in size between a longer direction and a shorter direction, and includes a curved outer edge portion (45; 145; 245; 345) in which at least a portion of an outer edge portion of the thin portion (42; 142; 242; 342) at both ends, or near both ends, in the longer direction is formed so as to be curved; wherein the fracture groove portion (50; 150; 250; 350) includes a center straight groove portion (60; 160; 260; 360) that extends in the longer direction of the thin portion (42; 142; 242; 342) in a center portion of the thin portion (42; 142; 242; 342), and a pair of side groove portions 70; 170; 270; 370), each of which is formed on either side in the longer direction of the center straight groove portion (60; 160; 260; 360) and connected to a corresponding longer direction end portion (60A, 60B; 160A, 160B; 260A, 260B) of the center straight groove portion (60; 160; 260; 360); and at least a portion (74; 174; 274; 374) of the side groove portions (70; 170; 270; 370) is formed so as to be curved following the curved outer edge portion (45; 145; 245; 345), characterized in that the side groove portions (70; 170; 270; 370) become thicker in a continuous or stepped manner farther away from the center straight groove portion (60; 160; 260; 360). an electrode body that forms a positive electrode and a negative electrode; an electrolyte; and a sealed case that houses the electrode body and the electrolyte, wherein a safety valve (40; 140; 240; 340) that opens when internal pressure of the case rises to equal to or greater than a predetermined value is formed in a portion of the case; wherein the safety valve (40; 140; 240; 340) includes a thin portion (42; 142; 242; 342) formed thinner than the surrounding portion of the safety valve (40; 140; 240; 340), and a fracture groove portion (50; 150; 250; 350) formed in the thin portion (42; 142; 242; 342); wherein the thin portion (42; 142; 242; 342) differs in size between a longer direction and a shorter direction, and includes a curved outer edge portion (45; 145; 245; 345) in which at least a portion of an outer edge portion of the thin portion (42; 142; 242; 342) at both ends, or near both ends, in the longer direction is formed so as to be curved; wherein the fracture groove portion (50; 150; 250; 350) includes a center straight groove portion (60; 160; 260; 360) that extends in the longer direction of the thin portion (42; 142; 242; 342) in a center portion of the thin portion (42; 142; 242; 342), and a pair of side groove portions 70; 170; 270; 370), each of which is formed on either side in the longer direction of the center straight groove portion (60; 160; 260; 360) and connected to a corresponding longer direction end portion (60A, 60B; 160A, 160B; 260A, 260B) of the center straight groove portion (60; 160; 260; 360); and at least a portion (74; 174; 274; 374) of the side groove portions (70; 170; 270; 370) is formed so as to be curved following the curved outer edge portion (45; 145; 245; 345), characterized in that the side groove portions (70; 170; 270; 370) become thicker in a continuous or stepped manner farther away from the center straight groove portion (60; 160; 260; 360).