The birth of management accounting was triggered by World War I. After the war, with the great change in market demand, the concept of management accounting was promoted by various managers and consulting firms to optimize production and sales through management accounting. Today, IT technology has evolved to the point where management accounting is required not only to explain past figures but also to contribute to future planning and management strategy. In this case study, we will introduce some examples of management accounting adopted by various companies in a before/after format.