ERP system has been spreaded from large companies to many small and medium sized companies, and it is recognized as a basic system for optimum and efficient work process. The focus is moving from manufacturing companies to various specialized companies. Once ERP system was introduced to those specialized companies, there was attempt to customize an ordinary system which used in manufacturing companies, but it was hard to take effect due to the lack of experience and an inadequate analysis of work process. Some of foreign ERP packages are possible to be constructed for some companies. However, they are originally aim at a large enterprise and it is also very difficult to construct and maintain. For this reason, small and midium sized companies are having a difficulty to construct ERP system. This study deals with the construction of ERP system for small and medium sized design engineering company and introduction of the crucial points throughout the construction and requirements for composition module and customization of each main module. Based on the findings of this study, the specialized non-manufacturing companies are expected to have efficient and practical application of ERP system when they select and customize the ERP package of manufacturing companies.