To realize the transmission of low load by avoiding the occurrence of a peeling sound (allophone) said to be a "Ji-Ji" sound by lowering the close contact degree with the surface of a pulley or enhancing the coefficient of friction in a flat belt.

The flat belt 1 is constituted by laminating an upper rubber layer 2, a core layer 3 and an under rubber layer 4, and the core layer 3 is formed by spirally winding a core cord 3b in an adhesive rubber 3a. The upper surface 2a and undersurface 4a of the belt becoming belt transmission surfaces are set to rough rubber surfaces having fine unevenness. These rough rubber surfaces are formed by using a vulcanizing mold 11 of which the molding surface (sleeve surface) is treated by shot blasting or a vulcanizing and molding rubber sleeve 18 subjected to shot blasting without performing post processing after vulcanizing molding.