A source code analysis unit identifies dependency strengths of one or more functions included in a source code. An influence analysis unit identifies one or more transfer functions that will each move to a different subsystem due to refactoring and identifies a dependency strength to be influenced by the refactoring, based on the dependency strengths that have been identified by the source code analysis unit with respect to the one or more transfer functions. A scale calculation unit calculates the scale of the refactoring, based on the dependency strength to be influenced, which has been identified by the influence analysis unit.