Abstract
The factors which worsen the system quality such as the increase on inaccurate requirements and misunderstanding of requirements due to the lack of communication has become increasing. In the case of maintenance phase, the complexity of source code increases due to the change of requirement and correcting errors. In these circumstances, the most important issue is how much the system engineers can fix the errors during the test phase. I introduce a case study of quality control activity by using the software metrics in maintenance phase.