A stud comprising: a body section in a columnar shape; a pin section disposed on one end of the body section along the central axis thereof; and a flange section disposed on the other end of the body section along the central axis thereof, wherein the pin section further comprises a pair of straight edge portions (31, 32) defined by peripheral edges of one end surface along the central axis, or peripheral profile lines in the cross section orthogonal to the central axis, opposite each other with the central axis therebetween, a pair of curved edge portions (33, 34) extending from the ends of the pair of straight edge portions (31, 32) and outwardly bulging away from each other with the central axis therebetween, and curved border edge portions (35, 36, 37, 38) between the straight edge portions (31, 32) and the curved edge portions (33, 34) outwardly bulging away from the central axis, a sectional shape of the body section orthogonal to the central axis and a shape of an end surface of the one end of the body section have a long axis and a short axis passing through the central axis and orthogonal to each other in the cross section orthogonal to the central axis, and the sectional shape of the body section and the shape of the end surface are symmetrical with respect to the long axis or the short axis as an axis of symmetry, and the maximum distance between curved edge portions (23, 24) of the body section intersecting with the long axis is defined as the major axis dimension, and the distance between straight edge portions (21, 22) of the body section intersecting with the short axis is defined as the minor axis dimension, four corners of a square are rounded by the curved border edge portions (35, 36, 37, 38) and a pair of sides opposite each other of the square are curved sides, the ellipticity of the sectional shape of the body section is greater than 0 and equal to or less than 0.2, where the ellipticity = 1 - (b/a), a is the major axis dimension, and b is the minor axis dimension, a sectional shape of the pin section orthogonal to the central axis has a long axis and a short axis passing through the central axis and orthogonal to each other in the cross section orthogonal to the central axis, and the sectional shape of the pin section is symmetrical with respect to the long axis or the short axis as an axis of symmetry, and the distance between the straight edge portions (31, 32) intersecting with the long axis is defined as the major axis dimension, and the distance between the curved edge portions (33, 34) intersecting with the short axis is defined as the minor axis dimension, and the ellipticity of the sectional shape of the pin section is 0.3 or more and 0.6 or less, where the ellipticity = 1 - (b/a), a is the major axis dimension, and b is the minor axis dimension. a body section in a columnar shape; a pin section disposed on one end of the body section along the central axis thereof; and a flange section disposed on the other end of the body section along the central axis thereof, wherein the pin section further comprises a pair of straight edge portions (31, 32) defined by peripheral edges of one end surface along the central axis, or peripheral profile lines in the cross section orthogonal to the central axis, opposite each other with the central axis therebetween, a pair of curved edge portions (33, 34) extending from the ends of the pair of straight edge portions (31, 32) and outwardly bulging away from each other with the central axis therebetween, and curved border edge portions (35, 36, 37, 38) between the straight edge portions (31, 32) and the curved edge portions (33, 34) outwardly bulging away from the central axis, a sectional shape of the body section orthogonal to the central axis and a shape of an end surface of the one end of the body section have a long axis and a short axis passing through the central axis and orthogonal to each other in the cross section orthogonal to the central axis, and the sectional shape of the body section and the shape of the end surface are symmetrical with respect to the long axis or the short axis as an axis of symmetry, and the maximum distance between curved edge portions (23, 24) of the body section intersecting with the long axis is defined as the major axis dimension, and the distance between straight edge portions (21, 22) of the body section intersecting with the short axis is defined as the minor axis dimension, four corners of a square are rounded by the curved border edge portions (35, 36, 37, 38) and a pair of sides opposite each other of the square are curved sides, the ellipticity of the sectional shape of the body section is greater than 0 and equal to or less than 0.2, where the ellipticity = 1 - (b/a), a is the major axis dimension, and b is the minor axis dimension, a sectional shape of the pin section orthogonal to the central axis has a long axis and a short axis passing through the central axis and orthogonal to each other in the cross section orthogonal to the central axis, and the sectional shape of the pin section is symmetrical with respect to the long axis or the short axis as an axis of symmetry, and the distance between the straight edge portions (31, 32) intersecting with the long axis is defined as the major axis dimension, and the distance between the curved edge portions (33, 34) intersecting with the short axis is defined as the minor axis dimension, and the ellipticity of the sectional shape of the pin section is 0.3 or more and 0.6 or less, where the ellipticity = 1 - (b/a), a is the major axis dimension, and b is the minor axis dimension.