  Site energy of the five-state ferromagnetic Potts model is numerically
calculated at the first-order transition temperature using corner transfer
matrix renormalization group (CTMRG) method. The calculated energy of the
disordered phase $U^{+}$ is clearly different from that of the ordered phase
$U^{-}$. The obtained latent heat $L = U^{-} - U^{+}$ is 0.027, which
quantitatively agrees with the exact solution.
