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: (d1) a deformable body portion ; (d2) a fixed portion that is provided on one end side of the body portion and is fixed to the socket ; and (d3) 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 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: (e1) an auxiliary inner peripheral seal portion that is slidable on the outer peripheral surface of the shaft portion ; (e2) an auxiliary dust seal portion that is slidable on the end surface of the annular member ; and (e3) 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 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: (d1) a deformable body portion ; (d2) a fixed portion that is provided on one end side of the body portion and is fixed to the socket ; and (d3) 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 (d1) a deformable body portion ; (d2) a fixed portion that is provided on one end side of the body portion and is fixed to the socket ; and (d3) 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 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: (e1) an auxiliary inner peripheral seal portion that is slidable on the outer peripheral surface of the shaft portion ; (e2) an auxiliary dust seal portion that is slidable on the end surface of the annular member ; and (e3) 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 in an axial direction. (d3-1) an inner peripheral seal portion 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 (e1) an auxiliary inner peripheral seal portion that is slidable on the outer peripheral surface of the shaft portion ; (e2) an auxiliary dust seal portion that is slidable on the end surface of the annular member ; and (e3) 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 in an axial direction. <EOS>