ACTIVE SONAR DEVICE

PROBLEM TO BE SOLVED: To provide an active sonar device capable of automatically detecting a detection limit distance and displaying a detectable range according thereto.SOLUTION: A control unit 130 for detecting a distance and an azimuth to a target on the basis of a search reception signal of a sonar transducer unit 110 includes: a noise data memory that retains a sonic wave from under water received by the sonar transducer unit 110 as noise data without transmitting the sound wave; and a level comparison computing unit that, when searching a target, compares a level of the search reception signal by the sonar transducer unit 110 with that of the noise data and calculates a point where the level of the search reception signal is same as the level of the noise data, as a detection limit distance. A display unit also displays a detectable range according to the detection limit distance.