An effective flood warning system is crucial for successful flood management. Flood warning systems have been developed in many countries across the world. However, scientific literature on flood warning systems has been mainly focused on technical capacity building, and the effectiveness of warning systems in mobilizing evacuation was much understudied. Japan is a country with a long history of fighting against flood disasters; the evaluation of its practices in providing flood warnings and the effectiveness are certainly important for further flood research development in Japan, and sharing the experience and lessons with the rest of the world will contribute to flood damage reduction on a global scale. Following this line of thinking, this article is intended to present a clear and concise picture of the current flood warning system in Japan, which has been poorly documented up until now. It is also aimed at providing a performance assessment for the flood warning system through case study approach and the use of Strengths, Weaknesses, Opportunities, and Threats (SWOT) model. Through analyses, the pros and cons of the current flood warning system in Japan are highlighted, and the directions for further development and refinement are explained.