A thin film transistor 100 according to the invention includes a gate electrode 20, a channel 44, and a gate insulating layer 34 provided between the gate electrode 20 and the channel 44 and made of oxide (possibly containing inevitable impurities; this applies to oxide hereinafter) containing lanthanum and zirconium. The channel 44 is made of channel oxide including first oxide containing indium, zinc, and zirconium (Zr) having an atomic ratio of 0.015 or more and 0.075 or less relative to indium assumed to be 1 in atomic ratio, second oxide containing indium and zirconium (Zr) having an atomic ratio of 0.055 or more and 0.16 or less relative to the indium (In) assumed to be 1 in atomic ratio, or third oxide containing indium and lanthanum having an atomic ratio of 0.055 or more and 0.16 or less relative to the indium (In) assumed to be 1 in atomic ratio.