Pressure reducing valves are widely used to maintain the pressure of gas reservoirs to specific values. In a normal valve, supply pressure is depressurized with an orifice plate. When pressurized air passes through the orifice plate, considerable noise occurs at the downstream side. To solve this problem, we have developed the slit structure that can maintain a laminar flow and can reduce the noise. At the former slit structure, the height of the slit was fixed. In this study, we proposed an improved slit structure that the height of slit is vari-able. Coned disk springs are installed between the slit structures and the height of them is precisely controlled. The flow characteristics of the slit are investi-gated theoretically and experimentally. The experimental results indicated that the noise level decreased by approximately 40dB.