To stabilize a belt pitch line, to reduce the generation of noise, and to improve a service life of a belt, in addition to improvement of the service life of the belt by preventing the generation of crack.

A material to be formed into a compression rubber layer 2 is wound around a cylindrical molding die 11 (inside die). A flat rubber sleeve is covered outside thereof, and semi-vulcanization is performed. The semi-vulcanization is performed in the condition wherein vulcanizing temperature is lower than that of the usual vulcanization and vulcanizing time is shortened. After the semi-vulcanization, a top surface side (a rubber part) of a semi-vulcanized article is cut, ground, or polished into a flat shape. After concluding cutting, grinding or polishing, the top surface side of the semi-vulcanized article is wound with a material to be formed into a core layer or an extended rubber layer to manufacture a belt forming body. A cog-shape rubber sleeve is covered outside the belt forming body formed on the molding die, and ordinary vulcanization is performed.