The purpose of this study is to examine how human errors which cause labor accidents occur and how they can be reduced to a minimum. In this study, two labor accidents caused by human errors were dealt with as case studies, in which we conducted semi-structured interviews with sixteen employees of a manufacturing company including victims, coworkers, maintenance workers, supervisors and managers. This study clearly states problems of the organization: maintenance delay of unstable facilities, managers’ ignorance of employees’ requests, attachment of importance to productivity, difficulty of evaluation of safety activities, and management of production line in a haphazard way. The result indicates what top executives, managers and supervisors should do to prevent human errors.