In the present invention, to make it possible to enhance the accuracy of positioning in an area not reached by a GNSS signal: a first position of a host device is estimated; the error of the first position is estimated; from a second device, other device information is received that includes a second position of the second device and a second error of the second position that have been estimated by the second device; and if the second error is smaller than the first error, the first position and first error are corrected on the basis of the other device information.