To prolong running lifetime of a belt by preventing a compressible rubber layer from being cracked even while running in a reversed bending state.

A core wire 3 comprising a code is buried in a binding rubber layer 2. An extensible rubber layer 5 is disposed in an upper portion of the binding rubber layer 2, and a compressible rubber layer 7 is also disposed in a lower portion thereof. A power transmission belt 1 whose periphery is covered with a cover canvas 4 includes both an upper rubber layer 9 and a lower rubber layer 10 in the compressible rubber layer 7. The lower rubber layer 10 has a smaller thickness than the upper rubber layer 9, and moreover, the lower rubber layer 10 is made of rubber compound having a higher thermal resistance than the upper rubber layer 9.