A ball joint including: (a) a ball stud that has a spherical portion at one end of a shaft portion; (b) a socket that has a bearing of the spherical portion and rotatably and swingably supports the ball stud; (c) an annular member that is fixed on an opposite side of the shaft portion to the spherical Portion; and a dust cover comprising: (d) a seal main body made of an elastic body and integrally having: a deformable body portion; a fixed portion that is provided on one end side of the body portion and is fixed to the socket; and a seal portion that is provided on another end side of the body portion and is provided so as to be slidable on the shaft portion and the annular member; and (e) an annular auxiliary seal made of resin and provided in the seal portion, wherein the seal portion includes: (d3-1) an inner peripheral seal portion (121a, 121b) that is slidable on an outer peripheral surface of the shaft portion; and (d3-2) a dust seal portion that is slidable on an end surface of the annular member, and characterized in that the auxiliary seal includes: an auxiliary inner peripheral seal portion that is slidable on the outer peripheral surface of the shaft portion; an auxiliary dust seal portion (152a, 152b) that is slidable on the end surface of the annular member; and a supported portion that is supported by a fixed member fixed to the shaft portion on an opposite side to the auxiliary dust seal portion (152a, 152b) in an axial direction. (a) a ball stud that has a spherical portion at one end of a shaft portion; (b) a socket that has a bearing of the spherical portion and rotatably and swingably supports the ball stud; (c) an annular member that is fixed on an opposite side of the shaft portion to the spherical Portion; and a dust cover comprising: (d) a seal main body made of an elastic body and integrally having: a deformable body portion; a fixed portion that is provided on one end side of the body portion and is fixed to the socket; and a seal portion that is provided on another end side of the body portion and is provided so as to be slidable on the shaft portion and the annular member; and a deformable body portion; a fixed portion that is provided on one end side of the body portion and is fixed to the socket; and a seal portion that is provided on another end side of the body portion and is provided so as to be slidable on the shaft portion and the annular member; and (e) an annular auxiliary seal made of resin and provided in the seal portion, wherein the seal portion includes: (d3-1) an inner peripheral seal portion (121a, 121b) that is slidable on an outer peripheral surface of the shaft portion; and (d3-2) a dust seal portion that is slidable on an end surface of the annular member, and characterized in that the auxiliary seal includes: an auxiliary inner peripheral seal portion that is slidable on the outer peripheral surface of the shaft portion; an auxiliary dust seal portion (152a, 152b) that is slidable on the end surface of the annular member; and a supported portion that is supported by a fixed member fixed to the shaft portion on an opposite side to the auxiliary dust seal portion (152a, 152b) in an axial direction. (d3-1) an inner peripheral seal portion (121a, 121b) that is slidable on an outer peripheral surface of the shaft portion; and (d3-2) a dust seal portion that is slidable on an end surface of the annular member, and an auxiliary inner peripheral seal portion that is slidable on the outer peripheral surface of the shaft portion; an auxiliary dust seal portion (152a, 152b) that is slidable on the end surface of the annular member; and a supported portion that is supported by a fixed member fixed to the shaft portion on an opposite side to the auxiliary dust seal portion (152a, 152b) in an axial direction.