Ground stations 20, 21 receive any signal transmitted by a geostationary artificial satellite 10, and store the reception signal together with the reception time thereof. A difference Δt in reception time of a same signal between the ground station 20 and the ground station 21 is calculated by performing correlation processing of the reception signal of the ground station 20 and the reception signal of the ground station 21. A distance R20 between the ground station 20 and the geostationary artificial satellite 10 is measured by a distance measurement device. A distance R21 between the ground station 21 and the geostationary artificial satellite 10 is calculated on the basis of the distance R20 obtained by measurement and the difference Δt in reception times, as obtained by correlation processing.