  To gain insights into mechanisms underlying superconducting transition in
copper oxide high-transition temperature ($T_c$) superconductors, we studied
transport properties of underdoped Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10+\delta}$
(Bi-2223) bulk single crystals. The power exponent $\alpha$ ($V \propto
I^{\alpha}$) reached 3 just below $T_c$, and the temperature dependence of
in-plane resistivity ($\rho_{ab}$) exhibited typical tailing behavior,
consistent with Kosterlitz--Thouless transition characteristics. Thus, with
increasing temperature, copper oxide high-$T_c$ superconductors undergo
transition to the normal state because of destruction of its phase
correlations, although a finite Cooper pair density exists at $T_c$.
