The case-based reasoning makes it possible to construct easy management mechanism for manipulating knowledge resources successfully. Some prototyping systems have been developed and applied to individual domains. However, it is important to structuralize effectively the organization in point of retrieval efficiency. In this paper, the structuralization method is addressed. Our structuralization method is characterized with regard to two concepts: categorization with knowledge about concept hierarchy; and organization based on the common features among two or more attributes. Our case categorization structure is represented by a direct acyclic graph, and can be organized automatically on the basis of the above concepts. This paper describes a case structuralization method and evaluates the retrieval efficiency through experiments.