To provide a method for manufacturing a transmission belt which has an excellent side pressure resistance and a reduced noise at the time of running and in which recycling of a scrap rubber is performed, a cutting time is shortened, a cutting resistance is reduced, the rubber is accurately V-groove finished.

The method for manufacturing the transmission belt comprises a step of molding a short fiber oriented rubber sheet 18 in which short fiber is oriented in a width direction, a step of molding a belt molding 58 by sequentially winding a belt constituting member and the short fiber oriented rubber sheet 18 cut in a predetermined length on a cylindrical molding mold 50, a step of notching rib grooves 19 extended in the longitudinal direction on the sheet 18 of the molding 58 by a V-shaped cutter blade 30 for imparting an ultrasonic vibration, a step of winding an outer mold 55 so as to engage the protrusion 56 of the mold 55 of a sheet-like rubber mold with the rib grooves 19 of the sheet 18, and a step of finishing a belt sleeve by vulcanizing the molding.