  In an extension of the Standard Model with a scalar color octet, the
possibility of the strongly first-order electroweak phase transition is
studied, by examining the finite-temperature effective Higgs potential at the
one-loop level. It is found that there are wide regions in the parameter space
that allow the strongly first-order electroweak phase transition, where the
Higgs boson mass is larger than the experimental lower bound of 115 GeV, and
the masses of the scalar color octet is around 200 GeV. The parameter regions
may be explored at the LHC with respect to the electroweak phase transition.
