Underground spaces are enclosed spaces that collect aboveground floodwater, which causes the inundation height to rise rapidly and thus makes them extremely dangerous spaces from the standpoint of water disasters. Due to the changing rainfall patterns in recent years, incidences of inundation damage to underground spaces have increased. In this situation, the Ministry of Land, Infrastructure, Transport, and Tourism of Japan revised the Flood Control Act in May 2015. This paper provides an overview of this latest revision.