To provide a method for manufacturing a transmission belt such as a V-ribbed belt, a double ribbed belt or the like having an excellent side pressure resistance by shortening a cutting time, reducing a cutting resistance and accurately finishing a V-groove.

The method for manufacturing the transmission belt having an adhesive rubber layer in which a core wire is embedded along the longitudinal direction of the belt, and a ribbed part extended in the longitudinal direction of the belt adjacent to the rubber layer comprises a step of molding a short fiber oriented rubber sheet 18 in which short fibers are oriented in a widthwise direction, a step of molding a belt molding 58 by winding a belt constituting member 57 and the sheet 18 cut in the predetermined length on a cylindrical mold and finishing to a vulcanized belt sleeve 59, and a step of notching at least one or more rib grooves 27 extended in the circumferential direction on the vulcanized sleeve 59 by a V-shaped cutter blade 30 having an ultrasonic oscillation applied thereto.