To improve adhesive property of a nylon resin base material for a belt with a rubber and stratified separation property, and improve flexure fatigue property by setting a tension strength in a specified range in a temperature atmosphere and a deforming rate having specified values of a belt base material which extends to an uniaxial direction.

A rubber for composing a rubber layer 3 in which both surfaces of a flat belt 1 serving a nylon resin base material 2 as a core material is covered through an adhesive agent, may be formed of either natural rubber and synthetic rubber, or it may be used by a single substance of a rubber layer as the rubber layer 3, and a reinforced fiber base material may be interposed in the rubber layer 3. A belt nylon resin base material 2 which is oriented to be extending to an uniaxial direction, is not endurable for using as a belt when a tension strength is small, is stratificationally separated and broken easily when it is exceedingly large, and flexure resistance fatigue characteristic is reduced. The tension strength in the atmosphere of 23°C and a deforming rate of 5% is set as 4 to 10kg/mm2, and thereby, it is possible to improve flexure resistance fatigue characteristic and durability.