Recently, serious failures of complex IT systems are becoming social problems. Assurance case attracts an attention as a technique to assure the dependability of critical systems. We have proposed d* framework which is an extended assurance case notation based on the network of dependable actors. In this paper, The assurance case creation procedure that creates the assurance case from the collaboration diagram is proposed and the case study is performed using this procedure. In this case study, a result is described by d* framework.