A ball joint has a dust cover fitted onto the outer periphery of a socket formed into the shape of a cylinder with a bottom. The socket has a dust cover groove into which a socket-fitting portion of the dust cover is fitted, and a dust cover-recieving surface for supporting a socket-facing surface of the dust cover. The dust cover-recieving surface inclines toward the socket-facing surface while extending from the outer side toward the inner side. Radial projections are formed on the inner peripheral surface of the socket-fitting portion of the dust cover. An axial projection which projects toward the dust cover-recieving surface is formed on the socket-facing surface of the dust cover.