The present paper numerically clarifies the degree of multiple scattering effects, which has been believed to become significant at high frequencies more than several hundred gigahertz. The specific rain attenuation is evaluated directly from an extinction cross section of dielectric spheres. A set of small dielectric spheres are randomly allocated inside a big fictitious sphere by using Weibull raindrop size distribution model. In order to take account of the multiple scattering among raindrops, we employ the mode matching method based on vector spherical wave functions and its addition theorem. Numerical results are demonstrated for the root mean square deviation of the specific attenuation between the cases with and without multiple scattering terms. Contrary to general belief, the deviation is the highest at around the boundary between microwave and millimeter wave bands.