To suppress the occurrence of abnormal noise, when the back of a belt abuts on and engages with an idler pulley and to suppress the occurrence of vertical rupture of a valley portion between ribs and crack from the end of the belt.

A rubber layer is provided with an inner layer 6 provided with a rib portion and an elongation layer 5, arranged on the back side of the inner layer 6 and containing a short fiber 4 having a bent portion. The elongation layer 5 contains the short fiber 4 so that the rate of the mass of the short fiber 4 to the mass of a rubber is within a range from 4:100 to 35:100.