In order to detect setting defects of a self-piercing rivet in a self-piercing rivet setting machine, on a graph having X-Y coordinates representing a rivet driven stroke and a rivet driving load, a normal upper limit curve 37 defining the upper limit of a normal setting range and a normal lower limit curve 38 defining the lower limit of the normal setting range are plotted to detect a conventionally detectable setting defects. Further, a defect upper limit curve 39 and a defect lower limit curve 41 which are obtained from an additional setting defect different from the conventionally detectable setting defects are plotted between the normal upper limit curve and the normal lower limit curve, so that the additional setting defect is detected when a plotted curve 45 of actual-measurement data of a rivet under a rivet driving operation lies between the defect upper and lower limit curves.