To provide an underground storage apparatus and an underground storage method which prevents water jetting from the openings of a passage or reduces the force of the jet when the water level of water stored in a storage tank rises in the case of arranging the openings of a plurality of passages communicating with the storage tank, on the ground surface different in height.

The underground storage apparatus includes the storage tank 2 buried underground, and the plurality of passages serving for communication between the storage tank 2 and the ground surface 50. A partition part 5 having an opening 21a and a blocking member 7 for opening/closing the opening 21a is installed in each passage, and the blocking member 7 blocks the opening 21a when the water level in the passage reaches a specified height.