Owing to the changes in working conditions brought about by mechanization, the occupational causes of low back pain (LBP) have shifted from dynamic factors to static ones. In the train repair factory, however, the workers must operate in such narrow working spaces that it is difficult to use machines. Therefore, the workers must often move heavy materials by hand and perform their duties in unnatural postures. The author deals with health problems induced by LBP among workers engaged in locomotive repair. All of the workers (178) were examined by questionnaire, and 120 workers who were suffering from LBP or had taken sick leave on account of LBP were summoned for a medical examination. The questionnaire consisted of twenty items specially selected to evaluate the influence of LBP on activities in daily life. Twenty-five workers (14.0%) complained of continuous LBP, and 89 workers (50.0%) complained of occasional LBP. The workers in this factory had a higher prevalence of LBP than the workers in many other factories. The rate of complaints concerning LBP rose according to the increase in the frequency of unnatural postures and the handling of heavy materials during work. It was demonstrated that LBP had a harmful influence on activites in daily life.