  In this paper, we discuss dissipation process of the binary mixture gas in
the thermally relativistic flow \textcolor{red}{by focusing on the
characteristics of the diffusion flux}. As an analytical object, we consider
the relativistic rarefied-shock layer problem around the triangle prism.
Numerical results of the diffusion flux are compared with the
Navier-Stokes-Fourier (NSF) order approximation of the diffusion flux, which is
calculated using the diffusion and thermal-diffusion coefficients by Kox
\textit{et al}. [Physica A, 84, 1, pp.165-174 (1976)]. In the case of the
uniform flow with the small Lorentz contraction, the diffusion flux, which is
obtained by calculating the relativistic Boltzmann equation, is roughly
approximated by the NSF order approximation inside the shock wave, whereas the
diffusion flux in the vicinity of the wall is markedly different from the NSF
order approximation. The magnitude of the diffusion flux, which is obtained by
calculating the relativistic Boltzmann equation, is similar to that of the NSF
order approximation inside the shock wave, unlike the pressure deviator,
dynamic pressure and heat flux, even when the Lorentz contraction in the
uniform flow becomes large, because the diffusion flux does not depend on the
generic Knudsen number from its definition in Eckart's frame.
\textcolor{red}{Finally, the author concludes that the accurate diffusion flux
must be calculated from the particle four flow, which is formulated using the
four velocity distinguished by each species of particles.
