The purpose of this study was to examine the structure of identity during adolescence and adulthood, from the viewpoint of "relatedness", using the comparative method. Items based on definition (73 items) were administered to adolescents (211 subjects) and adult (345 subjects). Factor analysis yielded seven factors in adolescents and six factors in adult, and factor "caring for a friend" was found in the former and not in the latter. The result showed that friendship was a characteristic of adolescence.