To determine the present position of a PHS portable terminal in the manner of triangulation by use of the received field intensity of a radio wave transmitted from the PHS portable terminal to a PHS base station.

From three or more PHS base stations K1, K2, K3... for receiving the present position data and displaying the present position, which received the radio wave from a PHS portable terminal 12, a PHS control station 13 collects the received field intensities, and determines the position of the PHS portable terminal 12 by triangulation from the position data of three PHS base stations K1, K2, and K3 having the higher received field intensities, and transmits it as the present position data to the PHS portable terminal 12 through the PHS base station K1 having the maximum received field intensity.