The present invention aims at surely and efficiently calculating size tolerances of a plurality of parts constituting a structure with the configuration that includes a tentative size tolerance setting section setting tentative size tolerances of the plurality of parts based on design data of the structure and part information of the plurality of parts; a primary analyzing section calculating a quality of the structure and sensitivities of the plurality of parts based on the tentative size tolerances set by the tentative size tolerance setting section; a judging section judging whether or not the quality satisfies a desired quality which the structure demands; and a secondary analyzing section calculating, if the judging section judges that the quality does not satisfy the desired quality, the size tolerances of the plurality of parts using the sensitivities such that the structure satisfies the desired quality.