Through an empirical analysis of firms in Japan, this paper investigates to what extent the public interest and the private interest theories, respectively, explain the actual regulatory process. Our estimation findings are as follows. First, the explanatory power of the public interest theory is higher in non-public utility industries, while that of the private interest theory is higher in public utility industries. Second, rapidly growing industries become less regulated as they no longer need government protection. Third, highly competitive industries become more regulated so as to retain profit for individual companies. Fourth, price level has different implications among industries. The negative coefficient in non-public utility industries supports the public interest theory, while the positive coefficient in public utility industries supports the private interest theory.