Generalized numerical method, radiation element method by ray emission model, REM2, is applied to plane-parallel and anisotropic scattering participating media using the delta function approximation. The boundary can be specular and/or diffuse, and both collimated and diffuse incident irradiation can be specified on the boundary. REM2 can be applied to various thermal conditions in the medium and boundaries. Good agreement is obtained between the present numerical solutions using the delta function approximation and existing exact solutions, even for strong forward and back scattering media. The proposed method is applied to an anisotropic scattering participating medium with a specular surface. The effect of specular reflectivity of scattering layers subjected to obliquely collimated flux was investigated.