  The electronic structure of the ferromagnetic material CeRh$_{3}$B$_{2}$ is
studied by means of first-principles calculations with an emphasis on the
treatment of localized $4f$ states around Ce. Via the construction of an
effective spin model from electronic structure calculations, we estimated the
Curie temperature $T_{\rm C}$ of CeRh$_{3}$B$_{2}$ and found a specific
configuration of the electronic structure which explains the exceptionally high
measured value of $T_{\rm C} \sim 120$ K as well as the small saturation
magnetization and the topology of the Fermi surface. Present advance in the
understanding of the subtle nature of the $4f$-electron state in
CeRh$_{3}$B$_{2}$ that brings about the exceptionally high $T_{\rm C}$ should
be also of technological relevance to exploit the utility of Ce in rare-earth
permanent magnets.
