  The thermodynamical one-loop entropy $S^{TD}$ of a two-dimensional black hole
in thermal equilibrium with the massless quantum gas is calculated. It is shown
that $S^{TD}$ includes the Bekenstein-Hawking entropy, evaluated for the
quantum corrected geometry, and the finite difference of statistical mechanical
entropies $-Tr\hat{\rho}\ln\hat{\rho}$ for the gas on the black hole and
Rindler spaces. This result demonstrates in an explicit form that the relation
between thermodynamical and statistical-mechanical entropies of a black hole is
non-trivial and requires special subtraction procedure.
