An acoustic positioning device includes an acoustic emitter and receiver. The device emits a sequence of at least one first acoustic signal (S1) and one second acoustic signal (S2), separated by a time interval T, and to receive and measure the arrival phase φ1 of S1 and the arrival phase φ2 of S2. The device measures a relative displacement between the acoustic emitter and the acoustic receiver and determines the approximate difference (R2−R1)AUX between the distance R1 traveled by S1 between the acoustic emitter and receiver, and the distance R2 traveled by S2 between the acoustic emitter and the acoustic receiver, and calculates the relative displacement (R2−R1) between the acoustic emitter and the acoustic receiver as a function of the approximate difference (R2−R1)AUX, of the time interval T and of the arrival phases φ1, φ2 respectively of S1 and of S2.