Monitoring of delamination is indispensable for CFRP structures. It is, however, very difficult to detect a delamination visually. This demands a new structural health monitoring method. For aerospace structures, it is required to monitor a delamination before flight, and this means the monitoring system must detect the delamination without loading. In authors' previous studies, the delamination can be monitored with the electric resistance change method. The method provided excellent performance of estimations. The method, however, requires complicated electric circuits and uses a two-probe method: two-prove method includes effects of the electric resistance change at the electrodes. To resolve these problems, an electrical potential method is employed here. In the previous paper, the electrical potential method showed poor performance of estimations for delamination cracks located near the center of the specimen. The practical zigzag crack has large effect on the performance of estimation when the delamination locates at the center segment of the specimen. This problem is overcome by means of a two-stage monitoring method. The new method shows excellent performance of estimations on the basis of FEM analyses. In this paper, experiments are conducted to identify the delamination using this method. The applicability of this method is examined using the experimental data.