  We discuss the QCD critical point at finite density through the study of many
flavor QCD, in which two light flavors and Nf massive flavors exist. Performing
simulations of QCD with two flavors of improved Wilson fermions, we calculate
probability distribution functions of many flavor QCD at finite temperature and
density. The dynamical effects of massive flavors and the chemical potential
are added using the reweighting technique. From the shape of the distribution
functions, we determine the critical surface separating the first order
transition and crossover regions in the parameter space of the light and
massive quark masses and the chemical potentials. It is found that the critical
massive quark mass becomes larger as the chemical potential increases in (2+Nf)
flavor QCD. The indication to the (2+1) flavor QCD is then discussed.
