An optimization analyzing apparatus for a shape of a part of a structural body, the optimization analyzing apparatus configured of a computer and comprising: a part shape pattern setting device configured to divide a part of a structural body including a two-dimensional element and/or a three-dimensional element into a plurality of segments in an axis direction, change a height or width of a cross section of each of the segments divided, and set a part shape pattern; a rigidity analyzing device configured to perform plural kinds of rigidity analyses including a torsional rigidity analysis and a local rigidity analysis of the structural body in a state in which the part for which the part shape pattern has been set by the part shape pattern setting device is incorporated in the structural body and obtain any of: rigidity; improvement rate of rigidity; and improvement rate of rigidity per increased unit weight, of the structural body for each kind of the rigidity analyses, the rigidity analyses comprising constraining one or more predetermined portions of the structural body and applying a load to one or more portions other than the constrained one or more portions, and the improvement rate indicating a degree of improvement of the rigidity of the structural body after setting the part shape pattern in comparison with the structural body having a standard shape; a multivariate analyzing device configured to perform a multivariate analysis for each kind of the rigidity analyses where any of the rigidity, the improvement rate of rigidity, and the improvement rate of rigidity per increased unit weight of the structural body that have been obtained by the rigidity analyzing device is a response variable and any of the height, the width, and a section modulus of each of the segments divided is an explanatory variable, and obtain a multiple regression coefficient, and a coefficient of determination or an adjusted R-square; a rigidity analysis selection device configured to select, based on any of the coefficient of determination and the adjusted R-square, any having strong correlation from among the rigidity analyses of the plural kinds; and a cross-sectional shape determination device configured to determine, based on the multiple regression coefficient, indicating a contribution to rigidity, calculated by the multivariate analyzing device in a rigidity analysis selected by the rigidity analysis selection device, an optimal cross-sectional shape of each of the segments divided. a part shape pattern setting device configured to divide a part of a structural body including a two-dimensional element and/or a three-dimensional element into a plurality of segments in an axis direction, change a height or width of a cross section of each of the segments divided, and set a part shape pattern; a rigidity analyzing device configured to perform plural kinds of rigidity analyses including a torsional rigidity analysis and a local rigidity analysis of the structural body in a state in which the part for which the part shape pattern has been set by the part shape pattern setting device is incorporated in the structural body and obtain any of: rigidity; improvement rate of rigidity; and improvement rate of rigidity per increased unit weight, of the structural body for each kind of the rigidity analyses, the rigidity analyses comprising constraining one or more predetermined portions of the structural body and applying a load to one or more portions other than the constrained one or more portions, and the improvement rate indicating a degree of improvement of the rigidity of the structural body after setting the part shape pattern in comparison with the structural body having a standard shape; a multivariate analyzing device configured to perform a multivariate analysis for each kind of the rigidity analyses where any of the rigidity, the improvement rate of rigidity, and the improvement rate of rigidity per increased unit weight of the structural body that have been obtained by the rigidity analyzing device is a response variable and any of the height, the width, and a section modulus of each of the segments divided is an explanatory variable, and obtain a multiple regression coefficient, and a coefficient of determination or an adjusted R-square; a rigidity analysis selection device configured to select, based on any of the coefficient of determination and the adjusted R-square, any having strong correlation from among the rigidity analyses of the plural kinds; and a cross-sectional shape determination device configured to determine, based on the multiple regression coefficient, indicating a contribution to rigidity, calculated by the multivariate analyzing device in a rigidity analysis selected by the rigidity analysis selection device, an optimal cross-sectional shape of each of the segments divided.