The effect of Application system with class units is not sufficient because of independency and reuse of Component elements due to component abstraction based on only source code. Therefore We need to apply design pattern approach to represent not only the problem abstraction but also information and relationship between system elements for generic solutions of specific domain, Also, it is essential to software reverse engineering acquiring the correct understandings of the system through examining the existing systems and utilizing the acquired knowledges as reusable resources. In this paper, the extraction algorithm with JAVA and the validity of applying reverse engineering with extracting design patterns from source codes of the existing object-oriented system; are devised. The architecture of automatic tool is designed and implemented for 1) automatic extraction of design patterns and 2) reuse tool for retrieving, editing and rebuilding of design patterns.