Abstract: A method and apparatus of forming a coating of a rubber or a synthetic resin having an even thickness on the external surface of a tubular textile jacket made of fibers woven or knitted in a tubular form, which comprises passing the tubular textile jacket through a bath of a coating liquid such as a latex solution or rubber paste or a synthetic resin, and then curing the liquid coating attached to the external surface of the jacket. The present method is characterized in that an expanding member capable of inflating the tubular jacket to almost a circular shape in its cross-section is packed into the interior space of the tubular textile jacket and maintained in a definite position with respect to the coating liquid, thereby keeping the jacket almost circular in its cross-section at least for a distance from the point where the tubular textile jacket departs from the bath of coating liquid to a point where the coating liquid attached to the external surface of the tubular jacket no longer is fluid.