PURPOSE: To surely and easily detect a defect point in a rubberized steel cord material for a tire structure part by performing detection by a magnetic field diffusion method.

CONSTITUTION: A detecting method is provided with a band-like steel cord 3 on it comprises 1-n numbers of detectors 1, and each detector 1 comprises one sensor and a usage tool. To inspect the cord 3 of 1m or less in width, at least three detectors 1 are adjacently assigned. A metal plate 2 above the detector 1 acts as a stage of the cord 3, and when a defect point 4 is inspected, the cord 3 is stretched beyond the metal plate 2. At that time, the gap between the cord 3 and the detector 1 is about 3mm, and a wire is provided in the lateral direction against the interlocking direction of the cord 3. Thus, when the defect point 4 comprising a single defective wire is stretched beyond the detector 1, a magnetic field changes to directly indicate it. Here, the cord 3 is stopped, and the defect point 4 is, for example, cut out for removal. Thus, only a perfect partially fabricated product is used for further manufacture for a tire.