For the improvement of residential environment of sound around a portal of a high speed train tunnel, model experiments for the reduction of MPW (Micro-Pressure Wave) have been studied for practical use. In order to reduce the level of MPW, a control wave, that is positive pressure, is generated at side-branch in the model tunnel and is superposed on the incident wave front of a compression wave propagating through the tunnel. The method of active reduction of MPW and experimental apparatuses are shown. Characteristics of the wave forms of the compression wave and the control wave with developed servo actuators were examined. The experimental results of the reduced level of MPW agreed well with numerical calculation results.