To manufacture a center belt for a high load transmission belt having trim surfaces having a uniform angle and no differences in level.

This high load transmission belt is constituted of a plurality of blocks fitted and fixed along the longitudinal direction of the center belt. In this manufacturing method for the center belt for the high load transmission belt having the trim surfaces having the angles on a block contact surface of the center belt, first grooves 46 for forming the trim surfaces on one surface of a center belt sleeve 45 are provided, second grooves 48 for forming the trim surfaces on the other surface are provided, and the block contact surface of the center belt is formed by subsequently cutting the center belt sleeve 45 into round slices at the first and second groove bottoms 50.