Abstract: A bending angle detection system capable of detecting a bending angle of a workpiece with high accuracy, wherein taking into account the fact that the brightness of a linear image formed on a surface of a workpiece is higher than that of a linear image formed on other areas than the workpiece, linear images picked up from the workpiece are automatically sorted out from linear images picked up from other areas according to differences in the brightness values of the linear images so that only the data representative of the linear images formed on the workpiece can be extracted.A linear projected light image formed on the workpiece surface is picked up by a CCD camera, a representative pixel of each scanning line on the picked up, multi-valued linear image is calculated by a representative pixel detecting unit.