It is hardly possible to install extremely high soundproof walls without reinforcing the viaduct drastically because the higher the soundproof wall IS, the greater the load and moment by wind becomes. Therefore, we have developed a new type of soundproof system. The developed system composes of transparent soundproof plate and frames supporting the plate. In this system, a rotary axis, and a11 support the soundproof plate or a part of three sides of it except the rotary axis are fixed by magnetic attractive force in ordinary state. 0n the contrary, when the wind load amounts to a limit of maintaining the safety of a viaduct, the plate opens and the wind load is reduced sufficiently. We have executed a load test, wind tunnel experiment and soundproof property test to verify the mechanism and property of the system with specimen in practical scale.