It is general to evaluate the strength of a structure by the strain and the stress obtained by using the finite element method. The strong shape can be derived for an overload when these evaluations are used. However, it is not an enough evaluation if it thinks from the viewpoint used in a mid/long term. In this paper, we propose the damage estimation algorithm which estimates the damage of the structure by using the structural analysis and the linear cumulative damage law. Finally, this proposal method is developed to the optimization problem, and we construct the optimization method of practical use which can design strong shapes corresponding to cumulative fatigue while estimating damage. The effectiveness of this proposed method is shown by applying to the shape optimization problem of the plunger tip in the die-cast process.