It is well known that the stresses concentrate in the discontinuity parts of the infinite plates or belt-such as semi-circle projections or notches, deep U-type notches and Neuber notches etc. But, in the case of infinite plates or belt having the complicated discontinuity parts, too-such as a cncave projections or convex notches etc. -, we can solve theoritically by using Schwarz-Christoffel's transformation, while hardly solve numerically, because the convergence of the series is not good. However, we can solve by using a special method to improve the convergence of the series and to calculate easily and smoothly the multiplication of series and series by the mechanical method. So, we calculate numerically in the case of such complicated shapes. At first, we calculate the edge stresses of the belt having a rectangular projection on one side and check these calculated values by the experiment of the photoelasticity-photograph, thus we got the good result.