This paper describes in detail the process from the rise of the market to the establishment of an oligopoly by NEC and its eventual collapse, focusing on the Japanese personal computer market from the late 1970s to the mid-1990s. This paper aims to find out why leader firms fail to respond adequately to innovations, which can significantly damage their competitiveness. In this paper, we will describe this case study more “thickly” than is normally required, based on the following three perspectives: (1) the process strategy perspective, (2) the competitive dynamics perspective, and (3) the action system approach perspective.