To provide a manufacturing method for a transmission belt which shortens a cutting time, lessens a cutting resistance and finishes a V-groove of high precision and makes the belt excellent in the resistance to lateral pressure.

The manufacturing method for the transmission belt comprises a process of molding a short-fiber oriented rubber sheet 18 having short fibers oriented in the width direction, a process wherein a belt component member and the short-fiber oriented rubber sheet 18 cut off in a prescribed length are wound on a cylindrical molding tool 50 and a belt molded body 58 is molded and finished to be a vulcanized belt sleeve 59 and a process wherein at least one or more rib grooves 19 extending in the circumferential direction are cut in the vulcanized belt sleeve 59 by a cutter blade 30 having a constitution wherein paired flat-blade knives 31 are shifted from each other in the cutting direction and tilted in the shape of a letter V so that the fore end parts thereof come close to each other and wherein the flat-blade knives 31 are made to conduct ultrasonic vibrations in the direction perpendicular to the cutting direction.