To perform position calibration, even if acoustic communication is not stable.

Acoustic positioning is performed from a support ship side, while an underwater vehicle is driven along each of paths 22, 23 for updating the latitude and longitudinal directions, when there is inertial navigation position does not have accumulated errors and has high accuracy. The representative value of the latitude component of the obtained acoustic positioning position 24a and the representative value of the longitudinal component of the acoustic positioning position 24b are set as a latitude direction reference value 25 and a longitudinal direction reference value 26, and thereafter, the underwater vehicle having the inertial navigation position having accumulated errors is driven again, along each of the paths 22, 23 for updating the positions in the latitude and longitudinal directions. The representative value 28 in the latitude direction of the acoustic positioning position 27a, obtained by the acoustic positioning from the support ship side and the representative value 29 in the longitude direction of the acoustic positioning position 27b, are compared with the reference values 25, 26 in the latitude and longitudinal directions to obtain variations δx, δy in the latitude and longitude directions. The inertial navigation position of the underwater vehicle is calibrated by the variations δx, δy.

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