The purpose of this study is to assess the organizational types and the job stress factors that affect the procedure-based job performances in nuclear power plants(NPPs). We derived 24 organizational factors affecting to the job stress in NPPs from the job stress analysis models of NIOSH(1989), Cooper(1990), and Karasek(1990). onsidering the safety characteristic in operating tasks of NPPs, we individuate among the tasks in NPPs through the division of duty and the analysis of cost activity. Through the questionnaire survey, a structured interview with the responsible employees, and expert panels, we assess 70 tasks among 777 tasks managed officially under the procedures. They are the representative tasks to the duties of each division and are directly related to the safety. We utilize the OPTI(organizational personality type indicators) to characterize the personality type of each organization in NPPs.