The present invention provides a thin film transistor using an oxide semiconductor as a channel, controlling threshold voltage to a positive direction, and realizing improved reliability. The thin film transistor includes: a gate electrode; a pair of source/drain electrodes; an oxide semiconductor layer provided between the gate electrode and the pair of source/drain electrodes and forming a channel; a first insulating film as a gate insulating film provided on the gate electrode side of the oxide semiconductor layer; and a second insulating film provided on the pair of source/drain electrodes side of the oxide semiconductor layer. The first insulating film and/or the second insulating film contain/contains fluorine.