A thin film transistor includes a gate electrode; a gate insulating film which contacts the gate electrode; an oxide semiconductor layer which includes a first region represented by In(a) Ga(b) Zn(c) O(d), wherein 0<a≦37/60, 3a/7−3/14≦b≦91a/74−17/40, b>0, 0<c<3/5, a+b+c=1, and d>0, and a second region represented by In(p) Ga(q) Zn(r) O(s), wherein q/(p+q)>0.250, p>0, q>0, r>0, and s>0, and located farther than the first region with respect to the gate electrode and which is arranged facing the gate electrode with the gate insulating film provided therebetween; and a source electrode and a drain electrode which are arranged so as to be apart from each other and are capable of being electrically conducted through the oxide semiconductor layer.