  The chiral phase transition at finite temperature T and/or chemical potential
$\mu$ is studied using the QCD-like theory with a variational approach. The
``QCD-like theory'' means the improved ladder approximation with an infrared
cutoff in terms of a modified running coupling. The form of
Cornwall-Jackiw-Tomboulis effective potential is modified by the use of the
Schwinger-Dyson equation for generally nonzero current quark mass. We then
calculate the effective potential at finite T and/or $\mu$ and investigate the
phase structure in the chiral limit. We have a second-order phase transition at
$T_c=129$ MeV for $\mu=0$ and a first-order one at $\mu_c=422$ MeV for T=0. A
tricritical point in the T-$\mu$ plane is found at T=107 MeV, $\mu=210$ MeV.
The position is close to that of the random matrix model and some version of
the Nambu-Jona-Lasinio model.
