Image quality of digital chest radiography using FCR (Fuji Computed Radiography) was evaluated experimentally and clinically, comparing with the conventional radiography using regular film-screen system (F-S system). 1. In experimental study, Burger's phantom and Hawlet chart were used. The results were as follows: 1) Almost same amount of incident X-ray exposure was necessary for FCR to obtain the same resolution power as F-S system. 2) Contrast enhancement processing did not improve resolution power in FCR. It was improved by the processing of spatial frequency enhancement in the range of lower than 0.5 c/mm, but was decreased by the same processing in the range of higher than 0.5 c/mm. 2. In clinical study, chest radiograms of FCR and F-S system which were taken at the same day were evaluated. The results were as follows. 1) Firstly, the visibility of abnormal shadows which were classified into nine types was evaluated subjectively by two chest-radiologists. As the results, FCR was superior to F-S system in visibility of the lesions overlapping mediastinum and diaphragm, calcifications and bone lesions. FCR was, however, inferior to F-S system in visibility of ground glass shadows, fine reticular shadows and granular shadows. 2) In the second step, the detectability of those interstitial shadows was evaluated using ROC curve analysis. As the results, FCR was statistically inferior to F-S system in detectability of those interstitial shadows.