1. A method for differential diagnosis of a plurality of predetermined interstitial lung diseases, comprising: selecting a plurality of clinical parameters defining characteristics of a subject; selecting a plurality of radiographic descriptors comprised of predetermined features obtained from a radiographic chest image defining interstitial lung diseases characteristics; converting said plurality of clinical parameters and said plurality of radiographic descriptors into numerical expressions; transforming each of said numerical expressions into a number in a predetermined range; inputting said transformed numerical expressions into a plurality of successive neural networks; and diagnosing at least one of said plurality of interstitial lung diseases using said neural networks in accordance with said input expressions including: distinguishing between normal and abnormal patterns in said radiographic chest image using a first of said plurality of successive neural networks; distinguishing between said plurality of predetermined interstitial lung diseases and other diseases using a second of said plurality of successive neural networks; and distinguishing between said plurality of predetermined interstitial lung diseases using a third of said plurality of successive neural networks.