  We investigate the phase structure of (2+Nf)-flavor QCD, where two light
flavors and Nf massive flavors exist, to discuss the feasibility of the
electroweak baryogenesis in realistic technicolor scenario and to understand
properties of finite density QCD. Because an appearance of a first order phase
transition at finite temperature is a necessary condition for the baryogenesis,
it is important to study the nature of finite temperature phase transition.
Applying the reweighting method, the probability distribution function of the
plaquette is calculated in the many-flavor QCD. Through the shape of the
distribution function, we determine the critical mass of heavy flavors
terminating the first order region, and find it to become larger with Nf. We
moreover study the critical line at finite density and the first order region
is found to become wider as increasing the chemical potential. We discuss how
the properties of real (2+1)-flavor QCD at finite temperature and density can
be extracted from simulations of many-flavor QCD.
