To efficiently optimize a part of a structure cross-sectional shape when determining the structure cross-sectional shape by using a computer.

When preparing a structure cross-sectional shape, a computer sets a deformed shape in a structure cross-section of a plurality of natural vibration modes of a structural model having a reference structure cross-sectional shape as base sectional shapes, and performs the deformation processing of partially suppressing or emphasizing each of the base sectional shapes. Thereafter, the computer prepares one trial structure cross-sectional shape by executing the weighted addition of a deformed part of the base cross-sectional shape subjected to the deformation processing. Then, the computer performs the simulation of the performance of the structure by using the trial structure model to perform the performance evaluation of the trial cross-sectional shape. In this condition, the computer performs the performance evaluation by changing the weighting intensity to be used to the weighted addition, searching the trial cross-sectional shape in which the results of the performance evaluation satisfy the preset conditions.