To provide a water storage tank for emergency for securing potable water and/or water for fire-fighting and smoothly supplying the water even at the occurrence of an emergency state such as a long-term suspension of water supply due to the occurrence of an earthquake or a burst of a water main.

A pressure water tank 1 provided with a pressure air tank 2 in juxtaposition and formed in a sealed state in a line of a water pipe 8 is interposed to allow water to flow through, and emergency shutoff valves 9 are installed upstream and downstream of the pressure water tank 1 to form a constant water passing state, while the juxtaposed pressure air tank 2 can be connected to the pressure water tank 1 through an air supply pipe 6 to supply air. A pressure regulating valve of the air supply pipe 6 is operated when the emergency shutoff valve 9 is operated in an emergency, and pressure air is supplied to the pressure water tank 1 from the pressure air tank 2 so that water in the pressure water tank 1 becomes pressure water. A by-pass pipe 10 in which a by-pass valve 11 formed in a normally closed state is interposed, is provided in parallel with the pressure water tank 1. When requiring the support of materials due to the collapse or the like of a house, air is supplied from a pressure air valve 7 to utilize an air jack or the like.