To provide a high-load transmission belt prevented from swinging in the vertical direction when the belt goes out of a pulley in travel using the belt by avoiding a reverse-flexure, assuring a long life of the belt, and suppressing generation of noises.

The high-load transmission belt 1 is constituted by installing, in center belts 3a, 3b, a block 2 consisting of an upper beam 11 and a lower beam 12 joined with a pillar 13 and having a groove for insertion of the center belts, and projections 8 abutting to the adjoining blocks for preventing the belt from reverse-flexure are formed on at least one of the front and rear surfaces of the upper beam 11.