To provide an erosion control dam which prevents decrease or stop of the function as an erosion control dam and erosion of the seashore and also discharges clarified water or polluted water to the downstream side through a bypass way of the erosion control dam, and further presenting an excellent landscape.

Steel units having a sluice gate 5 and sand-discharge gates 8 are installed within an erosion control dam. Water flows usually on the sluice gate 5 and when sand is discharged, the sluice gate is raised and the sand- discharge gates 8 are opened. A bypass 7 is provided to guide the upstream water of the dam to the downstream side thereof. The clarified water taken from the upstream side of dam is discharged to the downstream river, bypassing the dam or the polluted water (eutrophicated water) flowing in from the upstream side of the dam is discharged to the downstream river, bypassing the erosion control dam.