To improve the time resolution in the measurement by an acoustic distance measuring system.

A first signal generator 1A and a second signal generator 1B are connected to a wave transmitter 2 so that the sound waves of two frequencies f1 and f2 can be transmitted from the wave transmitter 2. In the mean time, operators 4A and 4B of two systems are connected to a wave receiver 3, which receives the reflected signals. In the respective operators 4A and 4B, filters 5A and 5B, which can pass only the frequencies f1 and f2, are provided. Therefore, even if the sound wave of the frequency f2 is transmitted without waiting the receiving of the sound wave of the frequency f1, confusion is not generated in the operators, and the time resolution of the measurement can be improved.