A dust cover used in a ball joint, the ball joint including: a ball stud which has, at one end of a shaft part thereof, a spherical part and which has, at the other end of the shaft part thereof, a flange part; and a socket which has a bearing for the spherical part and which rotatably and swingably supports the ball stud, the dust cover including: a deformable body section; a fixed part which is provided at one end of the body section and which is configured to be fixed to the socket; and a seal section which is provided at the other end of the body section and which is configured to be slidable with respect to both the shaft part and the flange part, wherein the seal section includes: an inner peripheral seal part which is configured to be slidable with respect to an outer peripheral surface of the shaft part; a dust lip part which is configured to be slidable with respect to an end surface of the flange part; characterized in that said seal section further includes an auxiliary dust lip part which is configured to protrude toward the other end and which is provided on a radially inward side of the dust lip part, wherein said auxiliary dust lip part is configured to be slidable with respect to a curved surface connecting the shaft part to the flange part, and said auxiliary dust lip part includes an inclined surface with a diameter that increases toward a tip thereof, and the inclined surface is configured to slidably make close contact with the curved surface. the dust cover including: a deformable body section; a fixed part which is provided at one end of the body section and which is configured to be fixed to the socket; and a seal section which is provided at the other end of the body section and which is configured to be slidable with respect to both the shaft part and the flange part, wherein the seal section includes: an inner peripheral seal part which is configured to be slidable with respect to an outer peripheral surface of the shaft part; a dust lip part which is configured to be slidable with respect to an end surface of the flange part; characterized in that said seal section further includes an auxiliary dust lip part which is configured to protrude toward the other end and which is provided on a radially inward side of the dust lip part, wherein said auxiliary dust lip part is configured to be slidable with respect to a curved surface connecting the shaft part to the flange part, and said auxiliary dust lip part includes an inclined surface with a diameter that increases toward a tip thereof, and the inclined surface is configured to slidably make close contact with the curved surface. an inner peripheral seal part which is configured to be slidable with respect to an outer peripheral surface of the shaft part; a dust lip part which is configured to be slidable with respect to an end surface of the flange part; characterized in that said seal section further includes an auxiliary dust lip part which is configured to protrude toward the other end and which is provided on a radially inward side of the dust lip part, wherein said auxiliary dust lip part is configured to be slidable with respect to a curved surface connecting the shaft part to the flange part, and said auxiliary dust lip part includes an inclined surface with a diameter that increases toward a tip thereof, and the inclined surface is configured to slidably make close contact with the curved surface.