At a system subsidiary of a major credit card company, we implemented optimization of running costs due to unclear classification of system operation costs, with approximately 70% of costs being unclear. We reorganized the accounting items in the budget and standardized the granularity of the breakdown to identify high-cost areas, thereby promoting visibility into the cost structure. Additionally, we broke down contracts into elements based on quantity, quality, and unit price, and conducted vendor negotiations based on examples from other companies and market prices. Through meticulous adjustments, we achieved cost reductions amounting to hundreds of millions of yen.