1. A computerized design parameter managing method for managing design parameters used respectively in a two-dimensional CAD system and a three-dimensional CAD system, comprising: performing computerized separation of two-dimensional CAD data and three-dimensional CAD data used, respectively, which has been inputted in the two dimensional CAD system and the three-dimensional CAD system into geometrical information and attribute information; performing computerized setting up of arbitrary design parameters, by an inputting means for inputting direction of a designer, independently among design parameters used respectively in the two-dimensional CAD system and the three-dimensional CAD system into shared design parameters and non-shared design parameters, and providing the shared design parameters in a virtually shared state among the two-dimensional CAD system and the three-dimensional CAD system; performing computerized correlation of the separated attribute information with the shared design parameters set up into the virtually shared state; preparing an attribute correlation table, which correlates attribute information of shared design parameters of the two-dimensional CAD system and the attribute information of the three-dimensional CAD system through design parameters, regarding to the attribute information which is correlating the design parameter with a virtually shared state in the two-dimensional CAD data and the three-dimensional CAD data; performing computerized accessing and recognizing of the separated attribute information correlated with the shared design parameters set up into the virtually shared state among two-dimensional CAD data and the three-dimensional CAD data used respectively in the two-dimensional CAD system and the three-dimensional CAD system; performing, in a co-design mode, computerized management of geometrical information of the shared design parameters set up into the virtually shared state which are correlated with the accessed and recognized separated attribute information as objects with data compatibility in the two-dimensional CAD system and the three-dimensional CAD system; separately and independently performing management of geometrical information of the non-shared design parameters which are not correlated with the accessed and recognized attribute information from the geometrical information which is performed to manage as objects with data compatibility in the two-dimensional CAD system and the three-dimensional CAD system; retrieving existing attribute data in the attribute correlation table, recognizing geometrical information of the shared parameters correlated to the retrieved attribute data, and managing the geometrical information as an object of a cooperation design mode, wherein a relevancy between the geometrical information being an object of the attribute information and the attribute information is maintained separately; and performing bundling of the geometrical information of the two-dimensional CAD data in a virtually shared state and the geometrical information of the three-dimensional CAD data in a virtually shared state through design parameters based on the attribute correlation table, wherein three dimensional CAD data and two-dimensional CAD data are bundled for use in the two-dimensional CAD system and in the three-dimensional CAD systems; converting mutually the geometrical information between the two-dimensional space and the three-dimensional space and in order to interchange data between the two-dimensional CAD system and the three-dimensional CAD system which differ in geometrical dimensions in Euclidean space; and displaying information of the three-dimensional CAD data and information of the two-dimensional CAD data simultaneously on one display for use in development of a product.