PURPOSE: To localize the position of a sound source by a method wherein the depth of a sound wave and the distance between each of two passive receivers and the sound source are determined from reception signals of the two receivers.

CONSTITUTION: Signals 101 and 102 which are received by two receivers disposed at positions being apart by a prescribed horizontal distance from each other and located at a prescribed depth respectively are inputted to a distance calculating circuit from input terminals 1 and 2. Correlation computation circuit 21 and 22 receive these signals 101 and 102 and calculate autocorrelations, while a correlation computation circuit 23 calculates a mutual correlation function. Maximum position detecting circuits 24 and 25 receive signals 103 and 104 from the circuits 21 and 22 and calculate the maximum autocorrelations, while a maximum position detecting circuit 26 receives a signal 105 from thee circuit 23 and calculates the maximum mutual correlation function. A function computation circuit 27 executes computation, by using a prescribed formula, based on signals 106 and 108 and further on a sonic speed signal 109 from an input terminal 3 and depth signals 110 and 111 of the receivers from input terminals 4 and 5. By this method, the depth of a sound source and a horizontal distance therefrom can be determined.