Nowadays, workstyle reforms have been promoted and there is an issue in medical community that hospital physicians are working too long because of night shift. Hospital physicians usually work at night consecutively even after daytime work, and there are concerns regarding the decrease in their concentration which possibly contribute to medical errors. In this study, we investigated how much concentration would be decreased after night work for pediatricians and which factors would affect decrease in concentration. Psychomotor Vigilance Task (PVT) was carried out to investigate the decrease in concentrations of pediatricians in our hospital after night work from December 2018 to January 2019. We conducted a questionnaire with items that included frequency of call, how time was spent during night work, and subjects are residents or supervisors. PVT was also carried out on different day for control. PVT time was significantly delayed compared to control after night work in all seven subjects. The factors which affected PVT time were frequency of call and sleep time. Residents had more delayed PVT time, which supposedly could cause decrease in concentration. In this study, we showed quantitative decrease in concentration after night work. Especially, residents are susceptive to mental and physical task due to their immaturity, as they spend more time to see patients and less time to sleep. Hospital pediatricians should consider how to do shift work for their health and medical safety.