This study aims to clarify that latent accidents can be used to investigate the cause of actual accidents and to reduce the aged drivers' accidents. As the results of the investigation in Fukui Region, the criterion-related and construct validities of latent accident data are verified. And the accident characteristics of aged drivers are revealed through the analysis based on latent accident data. In order to reduce the aged drivers' accidents, it is necessary not only to improve the driving mind for safety but also to establish the traffic circumstances where human errors are hard to occur.