  Ferromagnetic transition in three-dimensional double-exchange models is
studied by the Monte Carlo method. Critical temperature $T_{\rm c}$ is
precisely determined by finite-size scaling analysis. Strong spin fluctuations
in this itinerant system significantly reduce $T_{\rm c}$ from mean-field
estimates. By choosing appropriate parameters, obtained values of $T_{\rm c}$
quantitatively agree with experiments for the ferromagnetic metal regime of
(La,Sr)MnO$_{3}$, which is a typical perovskite manganite showing colossal
magnetoresistance. This indicates that the double-exchange mechanism alone is
sufficient to explain $T_{\rm c}$ in this material. Critical exponents are also
discussed.
