Wide-angle X-ray scattering experiments for supercritical CO:! near the higher-order phase transition line on the isotherm at T = 308 K were carried out. Radial distribution functions were compared with that of the high-pressure liquid CO2. The results show that the higher-order phase transition line divides supercritical state into two phases, i.e., liquidlike and gaslike regions, from the viewpoint of the structure. Radial distribution functions, however, indicate that this phase transition is remarkably gentle even near the critical point.