“Guideline for Regulatory Agencies in Evaluating Contents of Root cause Analysis by Operators“ was enacted as the policy for new inspection system in Japan. The objective is to indicate the view point to verify the appropriateness of the corrective actions and pre ventive actions implemented by operators based on root cause analysis and its analysis results. This guideline is leading to take four points into special consideration for adequate application. They are encouragement of further activities of the operators, flexibl e interpretation of the intention, versatility of the analysis methods and concepts and consideration of no blame culture. Moreover, as view point for regulatory agencies, it indicates with special emphasis that neutrality of the analyzing party, objectivity of an alysis result, and logicality of the analysis method are ensured. This guideline shall be continuously reviewed through integration of lessons learned from active use in future.