We investigate the phase structure of lattice QCD for the general number of flavors in the parameter space of gauge coupling constant and quark mass, employing the one-plaquette gauge action and the standard Wilson quark action. Performing a series of simulations for the number of flavors N-F=6-360 with degenerate-mass quarks, we find that when N(F)greater than or equal to7 there is a line of a bulk first order phase transition between the confined phase and a deconfined phase at a finite current quark mass in the strong coupling region and the intermediate coupling region. The massless quark line exists only in the deconfined phase. Based on these numerical results in the strong coupling limit and in the intermediate coupling region, we propose the following phase structure, depending on the number of flavors whose masses are less than Lambda(d) which is the physical scale characterizing the phase transition in the weak coupling region: When N(F)greater than or equal to17, there is only a trivial IR fixed point and therefore the theory in the continuum limit is free. On the other hand, when 16greater than or equal toN(F)greater than or equal to7, there is a nontrivial IR fixed point and therefore the theory is nontrivial with anomalous dimensions, however, without quark confinement. Theories which satisfy both quark confinement and spontaneous chiral symmetry breaking in the continuum limit exist only for N(F)less than or equal to6.