A ball joint comprising: a ball stud which has a shaft-shaped stud portion and a ball portion formed at an end of the stud portion and having a spherical surface; a socket which has a holding portion for slidably accommodating the ball portion of the ball stud, a dust cover receiving surface extending from an outer periphery of the holding portion, and a stud penetration opening portion which communicates with the holding portion and through which the ball stud penetrates in such a manner that the ball stud can pivot; a tubular dust cover which is formed of an elastic material, one open end of which forms a socket fitting portion fitted onto an outer periphery of the stud penetration opening portion, the other open end of which is fitted onto an outer periphery of the ball stud, and which covers the stud penetration opening portion; and a retaining ring which tightens an inner periphery of the socket fitting portion fitted onto the outer periphery of the stud penetration opening portion, wherein the dust cover has a socket facing surface which is formed on the side toward the one open end of the dust cover on the end surface of the socket fitting portion such that the socket facing surface faces the dust cover receiving surface of the socket, wherein the socket facing surface is pressed against the dust cover receiving surface of the socket when the dust cover is attached to the socket, characterized in that the socket facing surface is a tapered, inclined surface which expands radially from the inner peripheral surface of the socket fitting portion, extends towards the dust cover receiving surface, and includes an inner taper portion, an annular axial projection and a taper flanged portion formed in this order from the inner peripheral surface of the socket fitting portion, wherein the annular axial projection occupies a portion of the socket facing surface in a radial direction thereof and projects toward the dust cover receiving surface; and at least a portion of the dust cover receiving surface of the socket, which portion extends inwards from a position at which the axial projection faces the dust cover receiving surface, is formed by an inclined surface which approaches the socket facing surface while extending inward from that position, wherein the inner taper portion of the socket facing surface of the dust cover is located inward of the annular axial projection and is formed by an inclined surface which extends from the inner peripheral surface of the socket fitting portion to the annular axial projection. a ball stud which has a shaft-shaped stud portion and a ball portion formed at an end of the stud portion and having a spherical surface; a socket which has a holding portion for slidably accommodating the ball portion of the ball stud, a dust cover receiving surface extending from an outer periphery of the holding portion, and a stud penetration opening portion which communicates with the holding portion and through which the ball stud penetrates in such a manner that the ball stud can pivot; a tubular dust cover which is formed of an elastic material, one open end of which forms a socket fitting portion fitted onto an outer periphery of the stud penetration opening portion, the other open end of which is fitted onto an outer periphery of the ball stud, and which covers the stud penetration opening portion; and a retaining ring which tightens an inner periphery of the socket fitting portion fitted onto the outer periphery of the stud penetration opening portion, wherein the dust cover has a socket facing surface which is formed on the side toward the one open end of the dust cover on the end surface of the socket fitting portion such that the socket facing surface faces the dust cover receiving surface of the socket, wherein the socket facing surface is pressed against the dust cover receiving surface of the socket when the dust cover is attached to the socket, characterized in that the socket facing surface is a tapered, inclined surface which expands radially from the inner peripheral surface of the socket fitting portion, extends towards the dust cover receiving surface, and includes an inner taper portion, an annular axial projection and a taper flanged portion formed in this order from the inner peripheral surface of the socket fitting portion, wherein the annular axial projection occupies a portion of the socket facing surface in a radial direction thereof and projects toward the dust cover receiving surface; and at least a portion of the dust cover receiving surface of the socket, which portion extends inwards from a position at which the axial projection faces the dust cover receiving surface, is formed by an inclined surface which approaches the socket facing surface while extending inward from that position, wherein the inner taper portion of the socket facing surface of the dust cover is located inward of the annular axial projection and is formed by an inclined surface which extends from the inner peripheral surface of the socket fitting portion to the annular axial projection.