We investigated whether conceptual developments about other disorders (visual defect, hearing disorder, orthopedic impaired, Down's syndrome) were progressing more nearly intentionally than its autistic disorders. 37 siblings who had their brothers or sisters with autistic disorder were interviewed. At the results, conceptual development of some other disorders was progressing significant than its autistic disorder. However, in the comparison in an individual, a delay significant to conceptual development of autistic disorder wasn't found. In addition, although the siblings had caught action of their brothers and sisters well, when the feature of an understanding on autistic disorder was examined, it was surmisd that it hadn't resulted in an understanding about the correspondence to it.