The direct-current potential difference method (DC-PDM) is known as one of the promising non-destructive methods to evaluate the crack in the conductors. This method utilizes the change in the current path or the potential difference which is caused by the crack. In the previous study, a method of three-dimensional evaluation of semi-elliptical crack on the back surface of plate was proposed and its theoretical validity and practical utility were shown based on the results of numerical analyses and experiments. In this study, the method is extended to the identification of semi-elliptical crack on the inner surface of pipe and the related electric field analyses are carried out by the finite element method. The results show that the crack on the inner surface of pipe can be evaluated by the proposed method based on the distribution of potential difference measured on the outer surface of pipe. The present extension will be very useful for various practical cases which are often seen in the piping of power-generating and petrochemical plants.