To simplify the execution of work by joining a rainwater storage pipe by a rubber band, and to simply take out sand and mud flowing into the rainwater storage pipe at a low cost.

A rainwater storage system has first to fifth rainwater storage pipes 12 installed at specified grades. Each pipe 12 is formed by connecting a plurality of internal-external surface flat corrugated pipes 18 made of synthetic resin in series by the rubber bands. Mud storage sections 22 are formed to the outflow-side ends 12b of the pipes 12, and buckets 24 are mounted on the storage sections 22. Rainwater can be stored in each pipe 12, and sand and mud also flow in when rainwater flows into the pipes 12 but sand and mud are carried to the lower side of the grade and flow into the buckets 24 arranged in the storage sections 22 because the pipes 12 are secured at the specified grades. Accordingly, the deposition of sand and mud in the pipes 12 can be prevented, and the buckets 24 in which sand and mud are stored can be pulled up from inspection holes 40a and the sand and mud can be taken out.