In an elastic ball joint dust cover structured such that a spherical head portion formed in one end of a ball stud is retained within a socket, a shaft in the other end of the ball stud is fastened to a knuckle, a large-diameter opening portion is fixed and retained to an outer peripheral surface of the socket, a small-diameter portion having a reinforcing ring embedded therein is retained to the shaft, the reinforcing ring is constructed by a tubular portion, and a flange portion extending from an end portion of the tubular portion toward the shaft, and is integrated with the small-diameter portion in such a manner that a side surface of the flange portion at a side of the knuckle and an inner peripheral surface of the flange portion facing a peripheral surface of the shaft are exposed.