The importance of software industry is rapidly increasing with the growth of Internet and the advent of digital economy. The purpose of this study is to research the impact of the copyright protection for securing producers and enhancing of producing on social welfare. The Korean government reformed the copyright law to enhance the copyright protection in 2000 and intensely controlled software piracy in 2001. However, copyright protection has much controversy in aspects of hindering social use of software. This study compared and analyzed the general equilibrium and the copyright protection for social welfare maximization in two cases when network externality exists or not, by assuming the simple demand and supply functions.