An object of the invention is to obtain a high-speed and high-accuracy radio-wave propagation characteristic forecasting system in combination with the launching method by correctly estimating a diffraction phenomenon when a ray passes the vicinity of an edge of a structure. To estimate a radio-wave propagation characteristic in accordance with the ray launching method, when a ray passes the vicinity of an edge of a structure, a diffracted wave is generated at the edge if the distance between the edge and the ray is smaller than the radius of a ray spread. Thereby, it is easy to combine the ray launching method with the conventional ray launching method and it is possible to estimate a high-speed high-accuracy radio-wave propagation characteristic also considering a ray diffracted wave.