It is needless to say that in order to implement a large-scale system such as a product model for shipbuilding, reusability and generality of the system is important. For improving reusability and generality, partialization of the system should be considered. So a product model composed of elements is discussed in this paper. To implement a system by elments, a scale of elments and a method of putting elements together should be considered. Thus two different types of elements are introduced in this paper. One is 'Product Information Element' to represent information such as parts, shapes, and so on. To deside a scale of 'Product Information Element', various information are divided into three layers. The other is 'Relation Element' which put 'Product Information Elements' together. In 'Relation Element', functions to extract information and to make information are described. At the end of this paper, a design supporting system for shipbuilding which is composed of elements proposed in this study are shown.