How can Corporate Social Entrepreneurship (CSE) be implemented in existing corporations? The objective of this study is to elucidate the mechanisms of CSE. A case study analysis of a social business established in a Japanese department store has yielded the following conclusions. Firstly, this study demonstrates that Corporate Social Entrepreneurial Intentions (CSEIs) can be explained through the lens of Social Entrepreneurial Intentions (SEIs) theory. The concept of CSEIs had not been previously investigated, and the applicability of SEIs theory had not been demonstrated. Secondly, the concept of CSEIs can be presented in relation to the elements of Corporate Entrepreneurship (CE) and demonstrated to have a mutual influence. The study indicated that the acquisition and accumulation of resources significantly impact and enhance CSEIs, which in turn lead to the creation of business opportunities and concepts. Thirdly, a clear picture was drawn of intrapreneurs who successfully implemented CSE through learning in practice. In other words, the study found that the main prerequisite for demonstrating CSE is the possession of business creation skills.