By using elliptical cylinders containing a homogenous volume conductor, the effect of antero-posterior distance of the trunk on the lead vector in the Frank system was investigated. The modified methods described below were found to improve normality and orthogonality in the lead vector of the Frank system when the antero-posterior distance of the trunk was short. 1. The connection of electrode M and F was disconnected. 2. The Shunt resistance of leads X and Z was changed in order to correct the distortion of lead vectors caused by variable antero-posterior distance of the trunk. The following results were obtained: 1. When the antero-posterior distance of the trunk decreased, the magnitude of lead vectors X and Z in the Frank system increased more than that of Y and, therefore, normality and orthogonality of this system deteriorated. 2. In my modified Frank system, as increase in the magnitude of the vector in lead Y and decrease in that of lead Z appeared, normality improved and orthogonality advanced only in lead Y.