To provide a tension transmission type heavy load transmission belt and its block capable of meeting conditions demanded as a heavy load transmission belt, on a high level while having sufficient strength even in the case of reducing block weight and performing high-speed rotation.

This heavy load transmission belt 1 comprises tension belts 3a, 3b and a plurality of blocks 2 provided at a prescribed pitch along the longitudinal direction of the tension belts 3a, 3b, wherein the block 2 in use has thermosetting resin provided as a coating material 2b on the surface of an insert material 2a formed of thermoplastic resin.