PURPOSE: To make divergence tendency of errors small and to make the measured signal to approach the accuracy of the position output, which is to become a reference value, by performing the estimation and correction of the errors in the form of feedback.

CONSTITUTION: At the time of signal receiving from a radio navigation set 5 and an NNSS6, the received position output and the estimated position output are compared with each other. Based on the output of the comparison, gyrocompass errors, log-speed errors, tidal-current speed errors and estimated position output errors are estimated by a statistical processing of variance. Based on the estimated values, the computation of an estimated position computing part DR3 is corrected and controlled. The position output of the radio navigation set 5 is compared with the position output of the NNSS6, and the error in the position output of the radio navigation is estimated. Based on the estimated value, the position output of the radio navigation set 5 is corrected. Thus the divergence tendency of the errors is made small, and the measured value is made to approach to the accuracy of the reference position output.