A prismatic secondary battery comprising: a battery case in a prismatic shape which includes a bottom wall part in a rectangular shape forming a bottom, a side wall part in a prismatic tubular shape forming a side wall, and an opening part being open upward at an upper end of the side wall part; and a battery cover which is welded to the upper end of the side wall part of the battery case and seals up the opening part, wherein: the battery cover has a blockage part which blocks up the opening part, a contact part which is in contact with the upper end of the side wall part continuously along an entire periphery at a position outside the blockage part, and a convex part with a prescribed height L, which projects from the blockage part toward the bottom wall part, and wherein a gap is provided between the side wall part and the convex part; cover thickness at the contact part is set greater than 1/2 of a cover thickness Tt of the blockage part and is less than cover thickness at the blockage part, and wherein a sum of the cover thickness of the contact part and the prescribed height L is set greater than the cover thickness of the blockage part; and the convex part is configured to extend continuously along an entire periphery of an inner surface of the side wall part. a battery case in a prismatic shape which includes a bottom wall part in a rectangular shape forming a bottom, a side wall part in a prismatic tubular shape forming a side wall, and an opening part being open upward at an upper end of the side wall part; and a battery cover which is welded to the upper end of the side wall part of the battery case and seals up the opening part, wherein: the battery cover has a blockage part which blocks up the opening part, a contact part which is in contact with the upper end of the side wall part continuously along an entire periphery at a position outside the blockage part, and a convex part with a prescribed height L, which projects from the blockage part toward the bottom wall part, and wherein a gap is provided between the side wall part and the convex part; cover thickness at the contact part is set greater than 1/2 of a cover thickness Tt of the blockage part and is less than cover thickness at the blockage part, and wherein a sum of the cover thickness of the contact part and the prescribed height L is set greater than the cover thickness of the blockage part; and the convex part is configured to extend continuously along an entire periphery of an inner surface of the side wall part. the battery cover has a blockage part which blocks up the opening part, a contact part which is in contact with the upper end of the side wall part continuously along an entire periphery at a position outside the blockage part, and a convex part with a prescribed height L, which projects from the blockage part toward the bottom wall part, and wherein a gap is provided between the side wall part and the convex part; cover thickness at the contact part is set greater than 1/2 of a cover thickness Tt of the blockage part and is less than cover thickness at the blockage part, and wherein a sum of the cover thickness of the contact part and the prescribed height L is set greater than the cover thickness of the blockage part; and the convex part is configured to extend continuously along an entire periphery of an inner surface of the side wall part.