To solve problems that a large quantity of heavy weights such as concrete and a steel material are used, and moreover, a very long period of time is required for execution from foundation work to construction of a dam body in a conventional erosion control dam, and also, there are such problems that a large quantity of excavated soil is generated and how the excavated soil is disposed and carried in the mountainous region.

The structure is characterized in that an area for catching flow-down matters is formed by arranging at least two piles apart at a prescribed interval in the direction perpendicular to a flow as a pile structure in the vicinity of a bent part of a river and a mountain stream. Among other things, it is characterized in that the flow-down matters with a declined flow speed are accumulated altogether by arranging the pile structure in the vicinity of the terminal point of the bent part.