A shape design optimization of the boom system in high ladder vehicle modeled by 3-dimensional finite elements is carried out. The structural analysis is performed using 3-D FEA (Finite Element Analysis) giving the results of displacements, stresses and natural frequencies. The section height and width of the boom is controlled by the FEA result data. The subproblem approximation method is implemented for the optimal shape based on displacement and principal stress. In the meantime, Lanzcos algorithm method is implemented in order to find the natural frequency of the system. The optimal models obtained by three different optimization processes are compared with the initial model and evaluated for economic conditions respectively. It is found that the different shape optimization processes give the different shape optimization results, which suggest their unique optimal shapes under their necessary design condition.