Credit risk management based on portfolio theory becomes popular in recent Japanese financial industry. But consideration and modeling of chain reaction bankruptcy effect in credit portfolio analysis leave much room for improvement even though the importance of the effect is recognized among credit analysis experts. That is partly because method for grasping relations among companies with limited data is underdeveloped. In this article, chance discovery method is applied to estimate structure of industrial relations that are to include companies' relations that transmit chain reaction of bankruptcy. The steps for the data analysis is introduced and result of example analysis with Japanese default events data of 2005 is presented