To provide a hermetically sealed type water storage apparatus for external filtration, etc., designed to simply ensure the advanced rearing environment for fishes by effectively utilizing a hermetically sealed type external filter.

The hermetically sealed type water storage apparatus 2 for the external filtration having an introduction cylindrical part 10 and an extended storage part 12 is installed in a water tank 1 for rearing aquatic organisms. A water intake 14 for taking in water in the water tank 1 is provided in the upper part of the introduction cylindrical part 10. The extended storage part 12 is arranged in such a state as to be extended in the width or the depth direction of the water tank 1 relatively to the introduction cylindrical part 10. The water introduced through the introduction cylindrical part 10 is stored in the extended water storage part 12. The stored water can be fed to the hermetically sealed type external filter installed on the outside of the water tank 1.