Compared the language development of infants of today and those of the former days (about 50 years ago). Method; (a) Subject-N.K. (A girl, born 26th December, 1961) (b) Daily record. Kubo's method: Recorded every word N.K. uttered for 3 weeks around her birthday from 9:00 a.m. to 10:00 a.m. (every 6 months). Results: The development of vocabulary from 2 to 4 years old. The trend of the contents of the noun from 2 to 4 years old. Conclusion: Comparing with Kubo's results, found those facts: (1) The peak of language development is seen earlier than before. (2) Development of the conjunction, regarded as the index of thinking development, is similar. Therefore the development of language of children is not so much changed in essence.