A ball joint comprising: a ball stud having a shank portion which includes a spherical portion at one end of the shank portion and has a flange portion; a socket having a bearing for the spherical portion and supporting the ball stud in such a manner that the ball stud rotates and swings; a joint member joined to the shank portion on an opposite side of the shank portion from the spherical portion with respect to the flange portion; and a dust cover integrally including a deformable bellows-shaped body portion made of an elastic body, a fixed portion made of an elastic body, the fixed portion being arranged on one end side of the body portion and fixed to the socket, and a sealing portion made of an elastic body and arranged on the other end side of the body portion, the sealing portion including an inner peripheral sealing portion configured to be slidable on a part of the shank portion on the opposite side of the shank portion from the spherical portion with respect to the flange portion, the sealing portion further including a cover portion continuously covering, within an outer wall surface of the flange portion, a radially outward tip end portion and a part of a portion that decreases in diameter from the tip end portion toward the spherical portion side, characterized in that: the body portion integrally includes, in a state where the dust cover is not deformed, a first mountain portion protruding radially outward on the fixed portion side, a second mountain portion protruding radially outward on the sealing portion side, and a valley portion provided between these mountain portions and recessed radially inward. a ball stud having a shank portion which includes a spherical portion at one end of the shank portion and has a flange portion; a socket having a bearing for the spherical portion and supporting the ball stud in such a manner that the ball stud rotates and swings; a joint member joined to the shank portion on an opposite side of the shank portion from the spherical portion with respect to the flange portion; and a dust cover integrally including a deformable bellows-shaped body portion made of an elastic body, a fixed portion made of an elastic body, the fixed portion being arranged on one end side of the body portion and fixed to the socket, and a sealing portion made of an elastic body and arranged on the other end side of the body portion, the sealing portion including an inner peripheral sealing portion configured to be slidable on a part of the shank portion on the opposite side of the shank portion from the spherical portion with respect to the flange portion, a deformable bellows-shaped body portion made of an elastic body, a fixed portion made of an elastic body, the fixed portion being arranged on one end side of the body portion and fixed to the socket, and a sealing portion made of an elastic body and arranged on the other end side of the body portion, the sealing portion including an inner peripheral sealing portion configured to be slidable on a part of the shank portion on the opposite side of the shank portion from the spherical portion with respect to the flange portion, the sealing portion further including a cover portion continuously covering, within an outer wall surface of the flange portion, a radially outward tip end portion and a part of a portion that decreases in diameter from the tip end portion toward the spherical portion side, characterized in that: the body portion integrally includes, in a state where the dust cover is not deformed, a first mountain portion protruding radially outward on the fixed portion side, a second mountain portion protruding radially outward on the sealing portion side, and a valley portion provided between these mountain portions and recessed radially inward.