This study aimed to develop and validate an emergency nursing-care patient satisfaction scale to measure patient satisfaction with emergency room (ER) nursing. Patient satisfaction scales for ER nursing have been validated without considering the perspectives of the healthcare system or cultural background of the country. Moreover, although nursing care is changing with COVID-19, no scale has been specifically designed to assess patient satisfaction with ER nursing. The study population included patients who visited five ERs in Japan (March to December 2021) (n = 135). The rating scales were provided to patients who visited the ER and gave consent, and the patients were asked to reply. In the process of validating the scale, exploratory and confirmatory factor analyses of the construct and criterion validity were conducted. The confirmatory factor analysis results showed a factorial structure consisting of four factors. The domain and summary scores demonstrated good-to-excellent internal reliability (Cronbach’s range = 0.81–0.89). This patient satisfaction scale was designed and validated from the perspective of the Japanese healthcare system and cultural backgrounds. This scale may be useful for developing assessments and interventions to improve patient satisfaction with ER nursing.