A thin-film transistor includes: a gate electrode; a gate insulating film disposed on the gate electrode; an oxide semiconductor layer disposed on the gate insulating film and having a channel region located to face the gate electrode; a channel protective layer disposed on the gate insulating film and the oxide semiconductor layer; and source and drain electrodes each connected to the oxide semiconductor layer through a connection hole formed in the channel protective layer, in which the oxide semiconductor layer has, in a part of the channel region, a narrow region with a narrower width than a width of the connection hole.