Recently, Assurance case has been used in order to improve system and software dependability. However, assurance case is difficult to write because of risk and safety standards have not been commonly defined, and plenty of risks are domain specific risk that arouses depending on the combinations of components and implementations. It is hard to assess and cover all of the risk at developing assurance case. In this paper we propose a method to convert risk flow management to assurance case, and a support tool for collecting keywords for them. Our proposed method it to apply possible risks from the threat-source to harm level along with the structure of the GSN (Goal Structural Notation) and convert it to adapt the notation automatically. These will support to assess the risk on assurance case before a severe engineering task of operational system. Our achievement is that new strategy to subdivide goals using risk.