We identified the factors related to affective occupational commitment among nurses in Japan by conducting a cross-sectional survey in 12 hospitals in the Tohoku and Kanto districts of Japan in 2013. Of the 4046 nurses in these hospitals, 1330 completed the self-report questionnaire (valid response rate: 32.9%). High job satisfaction, high professional autonomy, having a scholarship loan, and being married were strongly related to affective occupational commitment. Conversely, having a high effort-reward imbalance and fewer overtime work hours indicated a low level of such commitment. The findings suggest that professional autonomy and job satisfaction are key factors for developing affective occupational commitment. Programs that promote professional autonomy and make people feel more appreciated for their work should be created to improve such commitment, and it would be important to provide adequate organizational resources to increase job satisfaction and reduce effort-reward imbalance. The fact that longer working hours are related to affective occupational commitment suggests that excessive emotional commitment to one's occupation can lead to overtime work. Therefore, nurse managers should consider the staff's working situations more thoroughly.