To provide a manufacturing process of a center belt, which uses a vulcanization technique of placing a releasing film on a die so as to mold and vulcanize the center belt without applying a releasing agent on the die, thereby requires no releasing agent or labor to apply it, and further leaves no releasing agent on a finished belt.

A polyolefin releasing film is placed on a convexoconcave die, a covering canvas and a rubber sheet are laminated in this order and the vulcanization is carried out by heating and pressing, and thereafter, mold released; in the manufacturing process of the center belt for a high-load transmission belt fixedly fitted with a block.