PURPOSE: To perform the on-off operation of bottom valves independently by interlocking the bottom valve switchgears provided at the upper and lower parts of a tank with the bottom valves.

CONSTITUTION: Since bottom valve switchgears A that open and close the bottom valves 4 provided at the respective bottoms of a number of tank rooms are provided near the upper and lower parts of a tank 1 and an interlocking device B that interlocks these bottom valve switchgears A with the bottom valves 4 is provided, the on-off operation of the respective bottom valves 4 can be performed by the bottom valve switchgears A in both the upper and lower parts of the tank 1. In addition, since an emergency operation unit C is provided near the lower part of the tank 1, all bottom valves 4 can simultaneously be closed by this emergency operation unit C.