To prevent unintended opening of a sealing structure caused by an earthquake or the rise of inner pressure of a storage tank.

The foam chamber includes: a foaming chamber 3 which is set on a side wall of a tank body 13 of the storage tank with inner pressure of at least atmospheric pressure and in which fire-extinguishing foam B rises in the vertical direction; a foam releasing outlet 15 through which the fire-extinguishing foam passes in the horizontal direction toward the storage tank; and a shield part 11 disposed on a horizontal channel 25 through which the fire-extinguishing foam B passes toward the foam releasing outlet 15 for sealing between the foaming chamber 3 and the foam releasing outlet 15. The shield part 11 is a check valve structure formed of a strong material.