With increase of engine power, noises in a car caused by its air intake are increasing. In particular in a one-box-car, as compared with a passenger car, noises caused by the air intake are severe, because the distance between the air intake and the passenger is nearer and the space under the floor is narrower than those of a passenger car. To reduce the noises caused by the air intake, we developed a new type of silencer. The developed silencer is a hybrid between a bypass type and a side branch type silencer with an additional part consisting of a semi-transmitting diaphragm in the bypass pipe. By using the developed silencer to a one-box-car, we confirmed that it has the effect of reducing the air intake noises by 10 dB in the frequency range of 60-200 Hz.