The purpose of this paper is to present the employment relationship between professionals and Japanese organizations, by examining whether or not professionals can be core employees in Japanese companies from the viewpoint of a strategic human resource management theory. The lack of lifetime employment encourages the externalization by professionals. On the other hand, regardless of the lack of lifetime employment, companies assume that they can cultivate a long-term commitment from professionals because of their intellectual traits. Therefore, professionals are an essential resource for competitive advantage in Japanese companies. This paper will demonstrate that professionals can become core employees from the viewpoint of a strategic human resource management theory, in consideration of literature about professional characteristics. Furthermore, institutions and companies need to invest in life-long training and support for professionals, in order to retain their services. Therefore, the cultivation of professionalism is required to achieve sustainable competitive advantage.