The WHOT-QCD Collaboration is pushing forward lattice studies of QCD at finite temperatures and densities using improved Wilson quarks. We first present results on QCD at zero and finite densities with two flavors of degenerate quarks (N(F) = 2 QCD) adopting the conventional fixed-N(t) approach. We then report on the status of a study of N(F) = 2 + 1 QCD adopting a fixed-scale approach armed with the T-integration method which we have developed.