The purpose of this study is to identify the relationships among the development level of expertise, education and training, qualifications and work experience for software developers. The main conclusions of this study can be summed up in four points. First, the expertise development level of software developers was highly influenced by analysis and design, project management, implementation, and testing, with an average of 3.0. Second, although software developers' expertise development ranks were most prominently divided into five classes, the developers of the highest class were extremely rare. Third, the newly measured variables in the level of expertise development, education and training, qualifications, and job career were highly affected by project performance, job experience, school education, and qualifications in that order. Meanwhile, it was found that the number of years of employment and the final education level in the standard variables of the unit price of labor varied depending on the measurement method. Fourth, it was confirmed that only the final education level was significantly determined by the developer's professional development grade, although the variables that could determine the development level of the developer's professionalism were the qualifications for project performance and job experience.