The product line is the remarkable technology that enables developing products quickly by instantiating product architecture from product line architecture according to product requirements. The product line architecture representing a common architecture of whole products in the product line is being regarded as an important asset in the product line. In order to easily create a product architecture from the product line architecture, common parts among products and variable parts of each product must be explicitly represented on the product line architecture. However, existing software architecture modeling languages, such as UML and ADLs, don? t support product line architectures in a helpful way. Therefore, we propose an approach to extension of UML 2.0 to represent variabilities on the product line architecture.