Internationally, it has been found that regular and timely hand washing is part of hand-hygiene practices that can reduce rates of infection in health-care facilities, but research has shown that there is a low level of compliance with hand washing in hospitals worldwide, including Japan. The number of aged-care facilities is growing throughout the world as our populations age, but hand-washing compliance appears even lower in such settings where there are vulnerable and frail elderly persons. This study used a correlational, cross-sectional design to clarify, for the first time, individual and facility factors related to the hand-washing behaviors of care staff at Japanese aged-care facilities. In 56 facilities (31 special nursing homes and 25 health-service facilities) in Yamaguchi Prefecture, data were gathered through survey questionnaires from care staff and facility managers. A total of 1323 (79.6%) questionnaires were returned and 1016 (61.1%) were analyzed. Using logistical regression analysis, two individual factors were investigated ("willingness to practice standard precautions" and "attendance at seminars") and two facility factors were investigated ("implementation of hand-washing evaluation" and "hand-washing environment"). These factors were found to promote hand washing, but no single factor was particularly related to its promotion in aged-care settings. If the health of elderly residents is to be better protected and infection rates lowered, especially in an era of increasing pandemics and epidemics, the compliance rate of health-care workers needs to be increased. We conclude that diverse approaches to both individual and facility factors are necessary to improve compliance with hand washing.