In this paper, we propose a wall position estimation method for indoor mobile robots having omnidirectional speakers and microphones. In this method, a linear up-chirp signal is emit from the speaker and recorded by the microphone, and an impulse response of the room is measured by calculating a crosscorrelation function between the transmit and receive signals. Furthermore, the distance to the wall surface is estimated by obtaining the delay time of the detected an echo. We implemented the proposed method on an indoor robot and experimented it, suggesting that it can estimate with an accuracy of 0.2 m.