Construction of cable-supported bridges using highstrength cables such as for cable-stayed bridges or suspension bridges is increasing,owing to the continuous developments in construction and structural analysis technologies.In particular,in the construction of a long-span bridge using cables,it is important to monitor the safety of the bridge by continuously measuring the cable tensile forces under the traffic use.Among the many measurement methods of the cable tensile forces,the vibration method of estimating tensile forces using the dynamic characteristics of the shape conditions of the cables is more economical and convenient than the direct method that measures the cable tensile forces using a load cell or a hydraulic jack,and is more popular these days.Recently,studies are being actively conducted to estimate cable tensile forces using an image measurement system,but such study results are being applied to regular inspections rather to a fixed system for long-term monitoring.Therefore,in this study,a vision-based monitoring system was developed that can estimate the dynamic characteristics of more cables using a single system unit.The developed vision-based monitoring system is equipped with a pan-tilt drive and zooming lens that are remotely controllable to estimate the dynamic responses of more cables positioned at a far distance using a single system unit,and was applied to a cable-stayed bridge,the three-span steel-concrete composite cable-stayed bridge of Busan-Geoje Fixed Link in South Korea,under the traffic use.