A secondary battery comprising: a battery element that includes a positive electrode, a negative electrode, and an electrolytic solution; a housing member that houses the battery element; and a safety valve mechanism that is attached to the housing member, wherein the safety valve mechanism includes a safety cover, a disk holder, a stripper disk and a sub-disk arranged in this order from the side farther from the battery element, wherein each of the safety cover, the disk holder, the stripper disk and the sub-disk has a substantially circular shape, wherein the safety cover includes an opening valve portion capable of being opened, wherein the stripper disk includes a plurality of ventilation holes which is radially arranged, in a region opposed to the opening valve portion, from a center of the region as a base point, and a plurality of protrusion portions which is radially arranged, in a region outside the plurality of ventilation holes, from the center as a base point and which protrudes toward the plurality of ventilation holes, the center of the region being a center of the stripper disk, wherein the plurality of ventilation holes and the plurality of protrusion portions are respectively arranged with a predetermined interval in a direction along an outer edge of the stripper disk, wherein a number of the ventilation holes and a number of the protrusion portions are equal to each other, and wherein each of the plurality of ventilation holes and each of the plurality of protrusion portions are opposed to each other in a direction toward the center such that the center position of each of the ventilation holes in the arrangement direction of the plurality of ventilation holes and the center position of each of the protrusion portions in the arrangement direction of the plurality of protrusion portions substantially coincide with each other, wherein the stripper disk comprises opening portions that are provided at positions where the stripper disk is partially removed, and the protrusion portions are formed at the remaining portions of an outer peripheral portion of the stripper disk, wherein the number of the ventilation holes is 6 or more and 8 or less, and wherein the number of the protrusion portions is 6 or more and 8 or less. a battery element that includes a positive electrode, a negative electrode, and an electrolytic solution; a housing member that houses the battery element; and a safety valve mechanism that is attached to the housing member, wherein the safety valve mechanism includes a safety cover, a disk holder, a stripper disk and a sub-disk arranged in this order from the side farther from the battery element, wherein each of the safety cover, the disk holder, the stripper disk and the sub-disk has a substantially circular shape, wherein the safety cover includes an opening valve portion capable of being opened, wherein the stripper disk includes a plurality of ventilation holes which is radially arranged, in a region opposed to the opening valve portion, from a center of the region as a base point, and a plurality of protrusion portions which is radially arranged, in a region outside the plurality of ventilation holes, from the center as a base point and which protrudes toward the plurality of ventilation holes, the center of the region being a center of the stripper disk, wherein the plurality of ventilation holes and the plurality of protrusion portions are respectively arranged with a predetermined interval in a direction along an outer edge of the stripper disk, wherein a number of the ventilation holes and a number of the protrusion portions are equal to each other, and wherein each of the plurality of ventilation holes and each of the plurality of protrusion portions are opposed to each other in a direction toward the center such that the center position of each of the ventilation holes in the arrangement direction of the plurality of ventilation holes and the center position of each of the protrusion portions in the arrangement direction of the plurality of protrusion portions substantially coincide with each other, wherein the stripper disk comprises opening portions that are provided at positions where the stripper disk is partially removed, and the protrusion portions are formed at the remaining portions of an outer peripheral portion of the stripper disk, wherein the number of the ventilation holes is 6 or more and 8 or less, and wherein the number of the protrusion portions is 6 or more and 8 or less.