In this study, we analyze and evaluate development data obtained in the course of "OMRON software Co.", that develops equipments used in financial markets, as well as data obtained during the development of software. Because of this, it is becoming very important for the softwaredevelopment corporations to find how to develop software efficiently while guaranteeing delivery time and quality, and holding down developing costs. Especially, estimating man-power of new projects and guaranteeing quality of software are important, because the estimation relates to costs and the quality relates to the reliability of corporations. In the field of embedded software, development techniques, management techniques, tools, testing techniques, reusing techniques, real time operating systems and so on have already been studied. However, there is few studies about the relationship between the development scales and the total errors using the data accumulated by past projects. Hence, we establish a model for the first trial to estimate the errors of a new project by using regression analysis.