1. A CAD supporting apparatus for supporting an assembling of an assembly by a CAD for assembling an assembly constituted of a plurality of components, which creates a geometry of objects, in cooperation with the CAD, said CAD supporting apparatus comprising: a data separating section for separating, upon receipt of CAD data representative of an assembly, which has a format suitable for being dealt with the CAD, from the CAD, the CAD data into structure data representative of a structure of the assembly, geometry data representative of a geometry of components constituting the assembly, and position data representative of a position of components on the assembly; an attribute set up section for setting up an attribute onto data separated by said data separating section in accordance with the operation; and a CAD data reconstruction section for creating CAD data representative of an assembly, which has a format suitable for being dealt with in the CAD, from data separated by said data separating section and reflecting the attribute set up by said attribute set up section, and for transmitting the CAD data created to the CAD.