Breather 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 and pressure fluctuation occur at the downstream side. To solve this problem, we have developed a slit structure that can maintain a laminar flow and can reduce noise and pressure fluctuation. In this paper, we newly develop a breather valve applied the concept of the slit structure. At the former slit structure, the compressed air enters from the center of the upper disk and is exhausted outward through the radial slits to the port. The height of the narrow radial slit was fixed. In the new valve, we proposed an improved slit structure that diameter is 50mm and the height of slit is variable. Coned disk springs, which diameter is 8mm, are installed between the slit structures and the height of them is precisely controlled with a pneumatic cylinder. The variable slit structure is installed in a breather valve instead of an orifice plate. As a result, the structure can successfully control the flow rate and control the pressure in a reservoir. The performance of the valve is investigated experimentally and confirmed that noise can be reduced with the slit structure.