A radio apparatus forming a radio network system calculates a calculated distance, based on a tentative self-position and tentative positions of a plurality of radio apparatuses existing in the vicinity. The radio apparatus successively and autonomously corrects the tentative self-position so that the calculated distance comes closer to the measured distance, relying more heavily on the calculated distance than the measured distance between itself and each of the plurality of radio apparatuses, and determines the position of itself. Other radio apparatuses also successively correct the tentative self-positions by the same method as the radio apparatus, and determine the positions of themselves.