Stepwise refinement in system-level design corresponds to restructuring an internal structure of a system while preserving functions of the system. We are aiming to build the restructuring process based on refactoring techniques. In this paper, we describe a restructuring procedure to obtain a concrete specification description from an abstract one. Moreover, we describe some existing refactorings used in restructuring steps and a new refactoring for system-level design. We designed a simple internet-router as an example. As a result, we obtained a specification model defined in the SpecC methodology from an abstract one. Moreover, our proposal shows that our research opens a new application field of refactoring, refactoring can be applied sufficiently to system-level design, and the refactoring can be the basis of stepwise refinement.