PURPOSE: To store purified rain water having a constant water pressure by constituting a U-shaped water-storing pipe from a plastic made inner and a cellular-resin made outer pipe, charging clarifying material into its horizontal portion, burying it under ground, and connecting a vertical portion with a rain gutter.

CONSTITUTION: A rain water storing device has a U-shaped plastic pipe 3 comprising a U-shaped synthetic-resin made inner pipe 1 and a cellular outer pipe 2 for covering outside thereof. The horizontal portion of the U-shaped plastic pipe 3 is buried underground, and the upper part of the vertical portion is connected with a rain gutter 4 of a house. Purifying material 6, such as activated carbon having a clarifying function, is accommodated in the horizontal pipe. Such stored water, because it has a required head pressure and is purified, is used as water for lives or water for disasters. Thus, utilization of rain water resources is carried out.