  Topological charge distributions of SU(3) gauge theory at finite temperature
are calculated on the lattice with high statistics in a manner of free from the
uncertainty of $\beta$-function. Clear temperature dependence of the
topological charge distribution is obtained. Combining the present result with
the recent study about the relation between the masses of $\eta$ meson system
and the gauge field topology, we obtain $m_{\eta'}(T)/m_{\eta'}(0) = 0.86 \pm
0.02$ and $0.69 \pm 0.01$ for $T=0.75 T_c$ and $T=0.93 T_c$, respectively. The
result shows the first clear evidence of the mass shift of $\eta'$ meson at
finite temperature.
