Aspect-oriented programming is the paradigm which extracts crosscutting concern from a system and solves scattering of a function and confusion of a code through software modularization. Existing aspect developing method has a difficult to extract a target area, so it is not easy to apply aspect mining. In an aspect minning, it is necessary a technique that convert existing program refactoring elements to crosscutting area. In the paper, it is suggested an aspect mining technique for extracting crosscutting concern in a system. Using abstract syntax structure specification, extract functional duplicated relation elements. Through Apriori algorithm, it is possible to create a duplicated syntax tree and automatic creation and optimization of a duplicated source module, target of crosscutting area. As a result of applying module of Berkeley Yacc(berbose.c) to mining process, it is confirmed that the length and volume of program has been decreased of 9.47% compared with original module, and it has been decreased of 4.92% in length and 5.11% in volume compared with CCFinder.