The effect of breadth on the frictional resistance of a flat plate can be explained by the boundary layer around edges of the plate. As the first approximation this may be obtained without considering an athwart flow induced by non-uniform thickness of the layer. To solve this problem, the authors showed that when the coordinate system is properly chosen the equations of motion can be reduced to a single equation in the direction of main flow, and that the elliptic coordinates are almost satisfactory to this condition. Thus the equation to be solved is simplified as eq. (4. 1) in this paper. The velocity distribution is obtained by the momentum transfer theory with some modifications corresponding to thd elliptic coordinates. Putting this velocity in the momentum equation, the frictional resistance of the plate is calculated as a function of its Reynolds number and aspect ratio. The results are shown in figs. 3, 4 and 5. Fig. 3 is the distribution of shearing stress in the athwart direction, Fig. 4 the experiments by several authorities, and Fig. 5 the percentage increase of the resistance.