I Purpose: As related to the problem,“what are the needs which a child tries to satisfy when he talks?”, J. Piaget studied the problem,“when children talk together, do they understand one another?” at La Maison des Petits de L'Institut J. -J. Rousseau at Geneva 1921-22. This problem is very important for us, beyond the difference between French and Japanese, because the modern trend of Japanese education stresses the importance of conversation among children. To find out children's mentality, we want to follow up Piaget's experiment faithfully, without reference to differences of languages. II Method of Experiment: 1. As materials of experiment we used two stories (pure language materials) and two descriptions of machine with visual aids. 2. Subjects; 20 pupils in 1st grade, 20 pupils in 2nd grade, 6 pupils in 3rd grade. Oike Elementary School, Toyonaka-shi, Osaka, 3. Equipment: A Taperecorder 4. Procedures of experiment: First of all, the experimenter gives pupil A (explainer) a brief story or a description of machine. pupil A (explainer) gives pupil B (reproducer) the same content. The experimenter records it with the taperecorder. He then makes pupil B to reproduce what he listens; the experimenter records it in the same way. The experimenter asks pupil A to explain what he has omitted. As a result, we find out the extent of children's understanding by measuring the following four points. a) How much the reproducer understood in relation to what the explainer had understood. d) How much the reproducer understood in relation to what the explainer had expressed. c) How much the explainer understood in relation to what the experimenter expressed. b) How much the explainer has expressed in relation to what he had understood. III Results: 1. We got almost same numerical results as Piaget's. 2. In terms of obscure and elliptical expression, lack of precision in the usage of pronoun, lack of order in stories, and juxtaposition of causalities of Piaget's theory of egocentrism, differences between a 6-7 years old child and a 7-8 years old child were also noticeable in this experiment. 3. But we could not find Jack of “effort to be objective” which Piaget observed in his results. 4. We can say that some differences exist between a 6-7 years old child and a 7-8 years old child. However, we can neither support nor deny Piaget's theory that the beginning of verbal understanding between children can be placed at approximately seven or eight years of age.