As IT-related projects become larger and more complex, it is difficult to successfully complete an IT project without high-level management capabilities. Accordingly, the Project Management Office (PMO), an organization specializing in project management to solve organizational, technical, and managerial problems related to project management, was introduced. The introduction of PMO is emerging as an important task for organizational development and project success, and PMO is a universal approach for IT project management. In this study, based on the PMO function researched by previous researchers, the proportion of public (defense) business managed through the introduction of a legal PMO system in the IT field and a separate dedicated management organization are required, as information systems have been expanded and the size of the input resources has increased. In addition, the important functions of PMOs in the private business sector are analyzed comprehensively through cases, and additionally, in the classification of direct management within the company by type of PMO and the type of consignment management, each important PMO function, and common important function are analyzed. Therefore, in this study, the important PMO function is verified regardless of industry field and organizational structure to help establish an effective PMO operation plan.