There is such experience as feeling incompetent in spite of one's outstanding accomplishments. Clance and Imes focused on this experience, and proposed a new concept "impostor phenomenon". In this study, researches on the impostor phenomenon were overviewed from the viewpoint of characteristics of the phenomenon, the trends of research before the proposal on it, its background, the relevant variables, and the measurement scales. As a result, it was revealed that there was ambiguity in the definition of the impostor phenomenon, in the significance of proposing this concept, and in the reality of it. In the future research, it is necessary to define the impostor phenomenon and to reveal the reality of it. Moreover, on the assumption that the impostor phenomenon as a state, its generation mechanism model was showed.