The purpose of this study is to clarify the meaning of openness and closedness of personality by reviewing studies on openness to experience (Rogers, 1959) and dogmatism (Rokeach, 1954), and to construct Experience Inventory (EI) for measuring an openness-closedness dimension. Thirty items of EI were selected on the basis of the pretest data. Five factors emerged as a result of the factor analysis (subjects were 740 university students, 114 junior college students and 202 high school students). Some examinations of EI test score proved that (a) EI had internal consistency and test -retestreliabilityand (b) theEItestscorewasnotinfluencedbysocialdesirability. Advocation of construct validity of EI was justified by (a) some significant relations between the EI test score and subscale score of mental health (self-actualizing) test,(b) some significant relations between the EI test score and subscale score of creativity test and (c) a piece of evidence that open-minded person had a high tendency of awareness and acceptance of the contradictory traits in him / herself.