As one of the lightweight software development methodology, the XP (Extreme Programming) is the practical means to improve the productivity and quality of software through the pursuit of 4 values - communication, simplicity, feedback, and courage. It appears, however, the TDD (Test Driven Development), one of the practices of XP, has a problem, which is the unavailability of the test driven development in case of the prolonged period of testing or the failure of securing the independency of the test cases. This results in the emphasis on the importance of the Mock Objects recently. The Mock Objects, the one imitating the faulty real code, has the fundamentals of simplicity allowing even manual script but, due to the inefficiency of manual script of the Mock Objects in a real life, it is implemented the Mock Objects Generator such as MockObjects, EasyMock in Java. It is found difficult, however, to apply the Mock Objects in C language due to its object-oriented premise as well as the absence of mock objects generators for C language. Therefore, in this paper, it is presented the CMock, a Mock Objects generator for C language which allows the easy creation of the Mock Objects, and the study is performed to verify the efficiency accordingly.