A method of coating a polymeric resinous thin film on the surface of a tubular braid reinforcing material, wherein a polymeric resinous coating material is spin coated on the surface of an annular braid, the coated braid is extruded into the air, and the coating material is coagulated in a coagulating bath, wherein the ratio of the spin coating feed ratio (Q) one the braid advancing speed (v) with respect to a unit outer diameter (D0) of the braid is represented by the formula k ⁡ ( g ⁢ / ⁢ m 2 ) = Q ⁡ ( g ⁢ / ⁢ min ) v ⁡ ( m ⁢ / ⁢ min ) ⁢ D 0 ⁡ ( m ) within the range of 200 to 3,000 g/m2.