This paper proposes a directive spectrum analyzing system using two microphones, one of which is fixed with the other revolving around the fixed one. The directivity pattern of the system can be arbitrarily changed by adjusting the delay time given to the microphones. A unibeam directivity is achieved when the outputs of the microphones are shifted so that both outputs are in phase for the incident sound from the specified direction. After giving the adequate delay time, the mean power spectrum and the mean cross power spectrum are computed during a full turn of the revolving microphone, and the power spectrum of the incident sound from the specified direction is estimated. The longer the distance between two microphones, the sharper the directivity is. This system is applicable to the case of many sound sources and is effective not only for the noise source detection in the noise control engineering but also for the underwater passive sonars.