For large companies, the renewal of the financial accounting system that supports core business operations is one of the most challenging projects. Even though the term "financial accounting system" is used in a single sentence, each company's accounting operations differ, and the required system functions and coverage will differ. In addition, large companies with large business and corporate scale have more points to consider when selecting a system, so it is necessary to understand the characteristics of their accounting operations before making a selection. In this document, we summarize the common "pitfalls" faced by large Japanese companies and present case studies of eight companies that have improved their business operations by selecting the most appropriate system for their company as hints for successfully implementing a financial accounting system, which is a challenging task.