PURPOSE: To obtain safely a reinforcing belt durable for a high load, by a method wherein the reinforcing belt is projected outside in a radial direction at the center or a crowning part of an axial direction before winding a beltlike body or a cord.

CONSTITUTION: After a steel belt material is assembled onto an assembling drum, a projected drum segment 22 is moved outside until the outside surface of its radial direction arrives at a position exceeding the circumference 20 at least partly. With this construction, an envelope curve of the circumference 26 is given by the central part 24 of the projected drum segment 22. Then an end part 25 of the outside of the radius direction of the projected drum segment 22 is moved to the outside of the radius direction up to a position where the same becomes precisely equal with the surface 23 of the outside of a flat drum segment 21. With this movement, a steel material is deformed into a projected state or a crownlike state. A rubber band or a cord containing a fiber cord is wound spirally round a bent steel layer.