To easily and accurately estimate the rigidity of each part of a vehicle body, to easily evaluate/manage the rigidity of each part and to make the most of the estimated rigidity to make optimum vehicle body design.

A real characteristic value analysis is used for an analysis model to obtain vibrational displacement at OHz in each vibrating mode, and vibrational displacement at the OHz of the analysis model is computed from the vibrational displacement to compute the rigidity of the analysis model. This rigidity is compared with a rigidity evaluation reference value to evaluate rigidity. When rigidity is insufficient, the minus degree of contribution of each vibrating mode is computed to show which vibrating mode causes insufficiency of rigidity, and distortion distribution plotting of the vibrating mode with the large minus degree of contribution is performed. Based on this, a countermeasure to a distortion concentrated part is taken.