The formant construction of Japanese vowels (/a/ / i/ /u/ /e/ /o/) was investigated by use of the sound spectrograph in 475 children ranging in age from 1 to 11. On the basis of these data the developmental process of vowel sounds was studied with special reference to shiftings in the vowel chart (a. b diagram.), which was proposed by M. Iri. The results and considerations were summarized as follows : 1) The formant construction in children was proved to be different from that in the adult,

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... cially in younger group of age from 1 to 4. 2) In children, each of three formants had a definitely higher absolute value than that of the adult. Among these three, there was a tendency that the first formant was relatively highest compared with that in the adult. 3) There was no sexual difference in the pattern of formant construction in all the subjects examined. 4) It was suggested that there were two directions in the developmental process of the vowel sounds; one direction was from middle to front, and the other was from middle to back. This result coincided with the tendency of vowel-like voices during prelinguistic period in Japanes infants.