Device to detect the tension for stretching machines and stretching machine adopting said device

Device (10) to detect the tension for stretching machines (11) comprising means (15) to feed at least a conductor (12), cable or optical fibre to be stretched, and at least a braking/traction device (16) which comprises at least a drum (17, 18) on which the conductor (12) is able to wind, and comprises at least a respective supporting shaft (22). On the shaft (22) in the detection device (10) at least an idle wheel (23) is coaxially assembled onto which the conductor (12) to be stretched winds before leaving the braking/traction device (16). At least a tension detection element (25) is positioned between the inner circumference of the idle wheel (23) and the outer circumference of the shaft (22).