Rainwater storage device and construction method thereof

A rainwater storage device comprising:

• a plurality of water storage pipes buried in a ground, the water storage pipes each having a rainwater inflow port on a surface of the ground;
• a lower connecting pipe that connects bottom part regions of the plurality of water storage pipes to each other;
• and
• an upper connecting pipe that is located above the lower connecting pipe and connects the plurality of the water storage pipes to each other, wherein:
• the plurality of water storage pipes is arranged in a plurality of rows and columns, extending in a predetermined direction as a first direction and a second direction intersecting the first direction, respectively;
• the lower connecting pipe is arranged in an inclined state toward one water storage pipe out of the plurality of water storage pipes;
• and
• the upper connecting pipe is arranged in an inclined state toward a direction opposite an inclined direction of the lower connecting pipe.