To provide an underground water enclosing/flowing system for enclosing contaminated soil and underground water with simple constitution and preventing the diffusion of contaminants following the rise of the underground water level due to rainfall or the like.

This system which surrounds the periphery of a contaminated area 50 contaminated with the contaminants A, by impervious walls 1A-1D extended to the hardly water permeable ground 53, is provided with a water collecting section 3 formed of a permeable layer for collecting underground water from the bottom part of the contaminated area 50; a storage section 4 for temporarily storing the underground water from the water collecting section 3, a discharge section 5 for discharging the underground water collected in the storage section 4; and a discharge facility 2 provided with a gate 6 for opening/closing the discharge section 5 to discharge the amount of rainfall permeation in the contaminated area 50 to the outside.