The steel cables are frequently used for various infrastructures. Especially, the steel cables in long span bridges such as cable stayed bridges and suspension bridges are critical members which suspend dead loads due to both the main girders and floor slabs. Damage at cable members can occur in the form of cross-sectional loss caused by corrosion and/or fracture, which can lead to structural failure due to concentrated stress of the cable. Therefore, nondestructive evaluation (NDE) of steel cables is needed so any cross-sectional damage can be detected. This study proposes a steel cable health monitoring technique using an elasto-magnetic (E/M) sensor installed in a cable climbing robot. The E/M sensor is applied to detect the cross-sectional loss in this study while it was originally developed for measuring the tensile force in the previous works. To verify the feasibility of the proposed damage detection technique, a series of experimental studies were performed. Firstly, a steel bars with 4-different diameters were fabricated and their output voltage values were obtained by the E/M sensor. The optimal input voltage and working point were chosen to ensure the linearity and resolution of the results through the repeated experiments. And then, the E/M sensor measured the output voltage values at the damage points of the steel bar specimen under the applied external and inner damage conditions based on the selected optimal experimental conditions. A final experiment was carried out with a steel cable which has corrosion damages to examine the capabilities of corrosion damage detection using E/M sensor, likewise experiments with steel bar specimen. This E/M sensor based monitoring technique will be incorporated into the cable climbing robot in the near further so that the proposed approach can be an effective automated NDE tool for steel cable health monitoring.