Author investigated safety accidents occurred in 26 companies during one year to study on the relationship between safety accident and shift systems.Safety accident incidence rate in 2-shifting system was 12.4 spells per 100 workers, was 1.7 times higher than 3-shifting system (7.3 spells) and 4 times than nonshift system (3.1 spells). The proportion of safety accident occurred by workers' mistake was 77.0 % at 3-shifting system, 68.8 % at 2-shifting system and 40.7 % at nonshift system. Safety accident incidence rate by workers' mistake in 2-shifting system was 8.5 spells per 100 workers, was 3.5 times higher than 3-shifting system (5.6 spells) and 5.3 times than nonshift system (1.6 spells). There was no fluctuation of safety accident incidence in nonshift system by time. But in 2- and 3-shifting system, spells of safety accident at the daytime were more higher than nighttime, vise versa spells of safety accident by workers' mistake. In nonshift system, a weekday of the most safety accident incidence was Thursday. But in 3-shifting system the most safety accident incidence was happened at weekend , vice versa in 2-shifting system. The proportion of admission by safety accidents was 44.6 % at 3-shifting system (33 spells) that was more higher than 2-shifting system (33.2 %) and nonshift system (22.4 %). Author concluded that safety accident incidences at shifting system were more higher than nonshift system and also more serious injuries were occurred. So the various comprehensive methods for the safety system, were needed to decrease the safety accident incidence and to increase worker's well-being.