  Pairing transition at finite temperature was investigated by the shell model
and BCS calculations. The definitive signature of pairing transition is
identified by a "transition temperature" $T_t$ estimated from a "thermal"
odd-even mass difference, while there is no sharp phase transition because of
the finiteness of nucleus. It is found that $T_t$ is in good agreement with
predictions of critical temperature $T_c$ in the BCS approximation, and the
pairing correlations almost vanish at two points of the transition temperature
$T\approx 2T_{t}$. The BCS calculations show that the critical temperature
$T_c$ increases with increasing deformation.
