A ball joint (100) to be fitted to a knuckle (200) is provided wherein, a shaft section (11) has an annular projection (11a), a dust cover (30) has a seal main body which is made of an elastic body and which integrally includes: a body section (31); a fixed section (32) which is provided in the body section (31) on one end side; and an inner circumferential seal section (33) and a dust seal section (34) which are provided in the body section (31) on another end side, and the ball joint (100) is provided with a positioning member (40) which is mounted to the shaft section (11) in advance before the ball joint (100) is fitted to the knuckle (200) and which positions an end of the dust cover (30) on the other end side with respect to the shaft section (11) so that the inner circumferential seal section (33) is positioned at an opposite side of the spherical section (12) across the annular projection (11a).