To provide a method and an apparatus for automatically tracking a target, which limits the position of the underwater target at a high accuracy from acoustic signals radiated from the target, thereby relieving the load on an operator.

An input circuit 2 converts only the required components of an acoustic signal received by a directional microphone 1 into a digital signal, a cepstrum circuit 3 calculates quefrency, an extractor circuit 4 detects the fundamental frequency from the calculated quefrency and converts to a frequency after line extraction, a function approximating circuit 5 calculates an approximate coefficient from the detected fundamental frequency, and a position/ depth estimating circuit 6 calculates the position, the depth and the expected CPA time of a target from the detected fundamental frequency and the velocity information of a target inputted to an information input circuit 7. Frequency spacing is automatically calculated to estimate the target position from an interference fringe, due to the time difference between the reflected wave and the direct input wave and hence the burden on the operator eases. The expected time and the position of the closes approach point to the microphone can be estimated.