The purpose of this study was to elucidate the changes and differences in mental activity status of nurses at a university hospital in Japan. We adopted the technology to monitor mind status by voice inputted from apps on iPhone and Android smartphones, which was developed by the members of the Center of Innovation (COI) of the University of Tokyo. The technology shows the long-term/short-term tendency of mind status, calculating emotional components contained in voice cord, feature of voice, and fluctuation pattern, which cannot be manipulated by person itself, involuntary reaction. After informed consent, we delivered apps implemented the technology to 33 nurses (male = 4, female = 29) belonging to the surgical ward of the university hospital in Tokyo and requested the participants to input their voices at the beginning and end of work shift for 14 days. We evaluated generation and age differences in mental activity status and changes between the beginning and end of work periods, between the day before a holiday and after a holiday, and between 16-h night shifts and day shifts. This study suggests the possibility of viewing mental activity status from voice noninvasively and supports the creation of healthy workplaces by predicting mental disorder.