Recent software system contains a lot of functions to provide various services. According to this tendency, it is difficult to ensure software quality and to eliminate crucial faults by conventional software testing method. Especially, in the conventional method, detail level of test items are widely deflected according with the engineers? skill, and this causes an immature software quality. In this paper, we discuss the effects of test engineer?s skill on test item generation, and propose a new test item generation method, that enables the generation of test items for illegal behavior of the system. The proposed method can generate test items based on Use-case analysis, deviation analysis for legal behavior, and faults tree analysis for system fault situations. From the result of the experimental applications, we confirmed that test items for illegal behavior of the system were effectively generated, and also the proposed method could effectively assist test item generation of poor skill engineer.